FOOTNOTES:

[1] Fulcher of Chartres, 1, i. For what follows, with regard to the

Church's conversion of _guerra_ into the Holy War, cf. especially the

passage--"Procedant contra infideles ad pugnam jam incipi dignam ...

qui abusive _privatum certamen_ contra fideles consuescebant

distendere quondam."

[2] Tradition credits a pope still earlier than Gregory VII. with the

idea of a crusade. Silvester II. is said to have preached a general

expedition for the recovery of Jerusalem; and the same preaching is

attributed to Sergius IV. in 1011. But the supposed letter of

Silvester is a later forgery; and in 1000 the way of the Christian to

Jerusalem was still free and open.

[3] The comte de Riant impugned the authenticity of Alexius' letter

to the count of Flanders. It is very probable that the versions of

this letter which we possess, and which are to be found only in later

writings like Guibert de Nogent, are apocryphal; Alexius can hardly

have held out the bait of the beauty of Greek women, or have written

that he preferred to fall under the yoke of the Latins rather than

that of the Turks. But it is also probable that these apocryphal

versions are based on a genuine original.

[4] Ekkehard, _Chronica_, p. 213.

[5] The _Chanson de Roland_, which cannot be posterior to the First

Crusade--for the poem never alludes to it--already contains the idea

of the Holy War against Islam. The idea of the crusade had thus

already ripened in French poetry, before Urban preached his sermon.

[6] Book i. c. iii. (in Muratori, _S.R.I._, v. 550).

[7] Ekkehard, _Chronica_, 214.

[8] Later legend ascribed the origin of the First Crusade to the

preaching of Peter the Hermit. The legend has been followed by modern

historians; but in point of fact Peter is a figure of secondary

importance.(See PETER THE HERMIT.)

[9] Godfrey's army numbered some 30,000 infantry and 10,000 cavalry

(Rohricht, _Erst. Kreuzz._ 61): Urban II. reckons Bohemund's knights

as 7000 in number (_ibid._ 71, n. 7).

[10] The Genoese had been invited by Urban II. in September 1096 "to

go with their gallies to Eastern parts in order to set free the path

to the Lord's Sepulchre."

[11] Thus already on the First Crusade the path of negotiation is

attempted simultaneously with the Holy War. On the Third Crusade, and

above all on the Sixth, this path was still more seriously attempted.

It is interesting, too, to notice the part which the laity already

plays in directing the course of the Crusade. From the first the

Crusade, however clerical in its conception, was largely secular in

its conduct; and thus, somewhat paradoxically, a religious enterprise

aided the growth of the secular motive, and contributed to the escape

of the laity from that tendency towards a papal theocracy, which was

evident in the pontificate of Gregory VII.

[12] Before he left, Raymund had played in Jerusalem the same part of

dog in the manger which he had also played at Antioch, and had given

Godfrey considerable trouble. See the articles, GODFREY OF BOUILLON

and RAYMUND OF TOULOUSE.

[13] For an account of the kings of Jerusalem see the articles on the

five BALDWINS, on the two AMALRICS, on FULK and JOHN OF BRIENNE and

on the LUSIGNAN (family).

[14] The genuineness of the letter (on which, by the way, depends the

story of Godfrey's agreement with Dagobert) has been impeached by

Prutz and Kugler, and doubted by Rohricht. It is accepted by von

Sybel and Hagenmeyer.

[15] Yet the north always continued to be more populous than the

south; and the Latins maintained themselves in Antioch and Tripoli a

century after the loss of Jerusalem. The land was richer in the

north: it was protected by its connexion with Cyprus and Armenia: it

was more remote from Egypt--the basis of Mahommedan power from the

reign of Saladin onwards.

[16] Pisa naturally connected itself with Antioch, because Antioch

was hostile to Constantinople, and Pisa cherished the same hostility,

since Alexius I. had in 1080 given preferential treatment to Venice,

the enemy of Pisa.

[17] This is the year in which the kingdom may be regarded as

definitely founded. The period of conquest practically ends at this

date, though isolated gains were afterwards made. The year 1110 is

additionally important by reason of the accession of Maudud al Mosul,

which marks the beginning of a Moslem reaction.

[18] Ilghazi died in 1122. His successor was Balak, who ruled from

1122 to 1124, and succeeded in capturing in 1123 Baldwin II. of

Jerusalem. The union of Mardin and Aleppo under the sway of these two

amirs, connecting as it did Mesopotamia with Syria, marks an

important stage in the revival of Mahommedan power (Stevenson,

_Crusades in the East_, p. 109).

[19] Maudud (the brother of the sultan Mahommed) may be regarded as

the first to begin the _jihad_, or counter-crusade, and his attack

expedition of 1113, which carried him so far into the heart of

Palestine, may be considered as the first act of the _jihad_

(Stevenson, op. cit. pp. 87, 96).

[20] Aleppo had passed from the rule of Timurtash (son of Ilghazi and

successor of Balak) into the possession of Aksunkur, 1125.

[21] Stevenson, however, believes that Zengi was _not_ animated by

the idea of recovering Jerusalem. He thinks that his principal aim

was simply the formation of a compact Mahommedan state, which was,

indeed, in the issue destined to be the instrument of the _jihad_,

but was not so intended by Zengi (op. cit. pp. 123-124).

[22] There are certain connexions and analogies between the kingdom

of Sicily and that of Jerusalem during the twelfth century. In either

case there is an importation of Western feudalism into a country

originally possessed of Byzantine institutions, but affected by an

Arabic occupation. The subject deserves investigation.

[23] The holders of fiefs (_sodeers_) both held fiefs of land and

received pay; the paid force of _soudoyers_ only received pay. An

instance of the latter is furnished by John of Margat, a vassal of

the seignory of Arsuf. He has 200 bezants along with a quantity of

wheat, barley, lentils and oil; and in return he must march with four

horses (Rey, _Les Colonies franques en Syrie_, p. 24).

[24] For the history of the orders see the articles on the TEMPLARS;

ST JOHN OF JERUSALEM, KNIGHTS OF; KNIGHTS, and the TEUTONIC ORDER.

The Templars were founded about the year 1118 by a Burgundian knight,

Hugh de Paganis; the Hospitallers sprang from a foundation in

Jerusalem erected by merchants of Amalfi before the First Crusade,

and were reorganized under Gerard le Puy, master until 1120. The

Teutonic knights date from the Third Crusade.

[25] As was noticed above, there were apparently separate assizes for

the three principalities, in addition to the assizes of the kingdom.

The assizes of Antioch have been discovered and published. The

assizes of the kingdom itself are twofold--the assizes of the high

court and the assizes of the court of burgesses. (1) The assizes of

the high court are preserved for us in works by legists--John of

Ibelin, Philip of Novara and Geoffrey of Tort--composed in the 13th

century. We possess, in other words, _law-books_ (like Bracton's

treatise _De legibus_), but not _laws_--and law-books made after the

loss of the kingdom to which the laws belonged. There are two vexed

questions with regard to these law-books. (a) The first concerns the

origin and character of the laws which the law-books profess to

expound. According to the story of the legists who wrote these

books--e.g. John of Ibelin--the laws of the kingdom were laid down by

Godfrey, who is thus regarded as the great [Greek: nomothetes] of the

kingdom. These laws (progressively modified, it is admitted) were

kept in Jerusalem, under the name of "Letters of the Sepulchre,"

until 1187. In that year they were lost; and the legists tell us that

they are attempting to reconstruct _par oir dire_ the gist of the

lost archetype. The story of the legists is now generally rejected.

Godfrey never legislated: the customs of the kingdom gradually grew,

and were gradually defined, especially under kings like Baldwin III.

and Amalric I. If there was thus only a customary and unwritten law

(and William of Tyre definitely speaks of a _jus consuetudinarium_

under Baldwin III., _quo regnum regebatur_), then the "Letters of the

Sepulchre" are a myth--or rather, if they ever existed, they existed

not as a code of written law, but, perhaps, as a register of fiefs,

like the Sicilian _Defetarii_. Thus the story of the legists shrinks

down to the regular myth of the primitive legislator, used to give an

air of respectability to law-books, which really record an unwritten

custom. The fact is that until the 13th century the Franks lived

_consuetudinibus antiquis et jure non scripto_. They preferred an

unwritten law, as Prutz suggests, partly because it suited the

barristers (who often belonged to the baronage, for the Frankish

nobles were "great pleaders in court and out of court"), and partly

because the high court was left unbound so long as there was no

written code. In the 13th century it became necessary for the legists

to codify, as it were, the unwritten law, because the upheavals of

the times necessitated the fixing of some rules in writing, and

especially because it was necessary to oppose a definite custom of

the kingdom to Frederick II., who sought, as king of Jerusalem, to

take advantage of the want of a written law, to substitute his own

conceptions of law in the teeth of the high court. (b) The second

difficulty concerns the text of the law-books themselves. The text of

Ibelin became a _textus receptus_--but it also became overlaid by

glosses, for it was used as authoritative in the kingdom of Cyprus

after the loss of the kingdom of Jerusalem, and it needed expounding.

Recensions and revisions were twice made, in 1368 and 1531; but how

far the true Ibelin was recovered, and what additions or alterations

were made at these two dates, we cannot tell. We can only say that we

have the text of Ibelin which was used in Cyprus in the later middle

ages. At the same time, if our text is thus late, it must be

remembered that its content gives us the earliest and purest

exposition of French feudalism, and describes for us the organization

of a kingdom, where all rights and duties were connected with the

fief, and the monarch was only a suzerain of feudatories. (2) The

assizes of the court of burgesses became the basis of a treatise at

an earlier date than the assizes of the high court. The date of the

redaction (which was probably made by some learned burgess) may well

have been the reign of Baldwin III., as Kugler suggests: he was the

first native king, and a king learned in the law; but Beugnot would

refer the assizes to the years immediately preceding Saladin's

capture of Jerusalem. These assizes do not, of course, appear in

Ibelin, who was only concerned with the feudal law of the high court.

They were used, like the assizes of the high court, in Cyprus; and,

like the other assizes, they were made the subject of investigation

in 1531, with the object of discovering a good text. The law which is

expounded in these assizes is a mixture of Frankish law with the

Graeco-Roman law of the Eastern empire which prevailed among the

native population of Syria.

In regard to both assizes, it is most important to bear in mind that

we possess not laws, but law-books or custumals--records made by

lawyers for their fellows of what they conceived to be the law, and

supported by legal arguments and citations of cases. But, as Prutz

remarks, Philip of Novara _lehrt nicht die Wissenschaft des Rechts,

sondern die des Unrechts_: he does not explain the law so much as the

ways of getting round it.

[26] For instance, the abbey of Mount Sion had large possessions, not

only in the Holy Land (at Ascalon, Jaffa, Acre, Tyre, Caesarea and

Tarsus), but also in Sicily, Calabria, Lombardy, Spain and France (at

Orleans, Bourges and Poitiers).

[27] One must remember that these reinforcements would often consist

of desperate characters. It was one of the misfortunes of Palestine

that it served as a Botany Bay, to which the criminals of the West

were transported for penance. The natives, already prone to the

immorality which must infect a mixed population living under a hot

sun, the immorality which still infects a place like Aden, were not

improved by the addition of convicts.

[28] The manorial system in the Latin kingdom of Jerusalem was a

continuation of the village system as it had existed under the Arabs.

In each village (_casale)_ the _rustici_ were grouped in families

(_foci_): the tenants paid from 1/4 to 1\3 of the crop, besides a

poll-tax and labour-dues. The villages were mostly inhabited by

Syrians: it was rarely that Franks settled down as tillers of the

soil. Prutz regards the manorial system as oppressive. Absentee

landlords, he thinks, rack-rented the soil (p. 167), while the

"inhuman severity" of their treatment of villeins led to a

progressive decay of agriculture, destroyed the economic basis of the

Latin kingdom, and led the natives to welcome the invasion of Saladin

(pp. 327-331).

The French writers Rey and Dodu are more kind to the Franks; and the

testimony of contemporary Arabic writers, who seem favourably

impressed by the treatment of their subjects by the Franks, bears out

their view, while the tone of the assizes is admittedly favourable to

the Syrians. One must not forget that there was a brisk native

manufacture of carpets, pottery, ironwork, gold-work and soap; or

that the Syrians of the towns had a definite legal position.

[29] After 1143 one may therefore speak of the period of the

Epigoni--the native Franks, ready to view the Moslems as joint

occupants of Syria, and to imitate the dress and habits of their

neighbours.

[30] Doubt has been cast on the view that a troubled conscience drove

Louis to take the cross; and his action has been ascribed to simple

religious zeal (cf. Lavisse, _Histoire de France_, iii. 12).

[31] We speak of First, Second and Third Crusades, but, more exactly,

the Crusades were one continuous process. Scarcely a year passed in

which new bands did not come to the Holy Land. We have already

noticed the great if disastrous Crusade of 1100-1101, and the

Venetian Crusade of 1123-1124; and we may also refer to the Crusade

of Henry the Lion in 1172, and to that of Edward I. in 1271-1272--all

famous Crusades, which are not reckoned in the usual numbering.

Crusades appear to have been dignified by numbers when they followed

some crushing disaster--the loss of Edessa in 1144, or the fall of

Jerusalem in 1187--and were led by kings and emperors; or when, like

the Fourth and Fifth Crusades, they achieved some conspicuous success

or failure. But it is important to bear in mind the continuity of the

Crusades--the constant flow of new forces eastward and back again

westward; for this alone explains why the Crusades formed a great

epoch in civilization, familiarizing, as they did, the West with the

East.

[32] This body of crusaders ultimately reached the Holy Land, where

it joined Conrad (who had lost his own original forces), and helped

in the fruitless siege of Damascus. The services which it rendered to

Portugal were repeated by later crusaders. Crusaders from the Low

Countries, England and the Scandinavian north took the coast route

round western Europe; and it was natural that, landing for provisions

and water, they should be asked, and should consent, to lend their

aid to the natives against the Moors. Such aid is recorded to have

been given on the Third and the Fifth Crusades.

[33] Manuel was an ambitious sovereign, apparently aiming at a

world-monarchy, such as was afterwards attempted from the other side

by Henry VI. As Henry VI. had designs on Constantinople and the

Eastern empire, so Manuel cherished the ambition of acquiring Italy

and the Western empire, and he negotiated with Alexander III. to that

end in 1167 and 1169: cf. the life of Alexander III. in Muratori, _S.

R. I._ iii. 460.

[34] The prize was won by Raynald of Chatillon (q.v.).

[35] Nureddin, unlike his father, was definitely animated by a

religious motive: he fought first and foremost against the Latins

(and not, like his father, against Moslem states), and he did so as a

matter of religious duty.

[36] Henry II., as an Angevin, was the natural heir of the kingdom of

Jerusalem on the extinction of the line descended from Fulk of Anjou.

This explains the part played by Richard I. in deciding the question

of the succession during the Third Crusade.

[37] The taxation levied in the West was also attempted in the East,

and in 1183 a universal tax was levied in the kingdom of Jerusalem,

at the rate of 1% on movables and 2% on rents and revenues. Cf. Dr A.

Cartellieri, _Philipp II. August_, ii. pp. 3-18 and p. 85.

[38] Stevenson argues (op. cit. p. 240) that this truce was already

practically dissolved before Raynald struck, and that Raynald's

"action may reasonably be viewed as the practical outcome of the

feeling of a party."

[39] The "economic" motive for taking the cross was strengthened by

the papal regulations in favour of debtors who joined the Crusade.

Thousands must have joined the Third Crusade in order to escape

paying either their taxes or the interest on their debts; and the

atmosphere of the gold-digger's camp (or of the cave of Adullam) must

have begun more than ever to characterize the crusading armies.

[40] The Crusades in their course established a number of new states

or kingdoms. The First Crusade established the kingdom of Jerusalem

(1100); the Third, the kingdom of Cyprus (1195); the Fourth, the

Latin empire of Constantinople (1204); while the long Crusade of the

Teutonic knights on the coast of the Baltic led to the rise of a new

state east of the Vistula. The kingdom of Lesser Armenia, established

in 1195, may also be regarded as a result of the Crusades. The

history of the kingdom of Jerusalem is part of the history of the

Crusades: the history of the other kingdoms or states touches the

history of the Crusades less vitally. But the history of Cyprus is

particularly important--and for two reasons. In the first place,

Cyprus was a natural and excellent basis of operations; it sent

provisions to the crusaders in 1191, and again at the siege of

Damietta in 1219, while its advantages as a strategic basis were

proved by the exploits of Peter of Cyprus in the 14th century. In the

second place, as the Latin kingdom of Jerusalem fell, its

institutions and assizes were transplanted bodily to Cyprus, where

they survived until the island was conquered by the Ottoman Turks.

But the monarchy was stronger in Cyprus than in Jerusalem: the fiefs

were distributed by the monarch, and were smaller in extent; while

the feudatories had neither the collective powers of the haute cour

of Jerusalem, nor the individual privileges (such as jurisdiction

over the bourgeoisie), which had been enjoyed by the feudatories of

the old kingdom. Till 1489 the kingdom of Cyprus survived as an

independent monarchy, and its capital, Famagusta, was an important

centre of trade after the loss of the coast-towns in the kingdom of

Jerusalem. In 1489 it was acquired by Venice, which claimed the

island on the death of the last king, having adopted his widow (a

Venetian lady named Catarina Cornaro) as a daughter of the republic.

On the history of Cyprus, see Stubbs, _Lectures on Medieval and

Modern History_, 156-208. The history of the kingdom of Armenia is

closely connected with that of Cyprus. The Armenians in the

south-east of Asia Minor borrowed feudal institutions from the Franks

and the feudal vocabulary itself. The kingdom was involved in a

struggle with Antioch in the early part of the 13th century. Later,

it allied itself with the Mongols and fought against the Mamelukes,

to whom, however, it finally succumbed in 1375.

[41] The kingdom of Jerusalem is thus from 1192 to its final fall a

strip of coast, to which it is the object of kings and crusaders to

annex Jerusalem and a line of communication connecting it with the

coast. This was practically the aim of Richard I.'s negotiations; and

this was what Frederick II. for a time secured.

[42] M. Luchaire, in the volume of his biography of Innocent III.

called _La Question d'Orient_, shows how, in spite of the pope, the

Fourth Crusade was in its very beginnings a lay enterprise. The

crusading barons of France chose their own leader, and determined

their own route, without consulting Innocent.

[43] As a matter of fact, there is some doubt whether Alexius arrived

in Germany before the spring of 1202. But there seems to be little

doubt of Philip's complicity in the diversion of the Fourth Crusade

to Constantinople (cf. M. Luchaire, _La Question d'Orient_, pp.

84-86).

[44] It is true that in 1208 Venice received commercial concessions

from the court of Cairo. But this _ex post facto_ argument is the

sole proof of this view; and it is quite insufficient to prove the

accusation. Venice is _not_ the primary agent in the deflection of

the Fourth Crusade.

[45] Already under Innocent III. the benefits of the Crusade were

promised to those who went to the assistance of the Latin empire of

the East.

[46] In 1208 Innocent excommunicated Raymund VI. of Toulouse on

account of the murder of a papal legate who was attempting to

suppress Manichaeism, and offered all Catholics the right to occupy

and guard his territories. Thus was begun the First Crusade against

heresy. Raymund at once submitted to the pope, but the Crusade

continued none the less, because, as Luchaire says, "the baronage of

the north and centre of France had finished their preparations," and

were resolved to annex the rich lands of the south. In this way

land-hunger exploited the Albigensian, as political and commercial

motives had helped to exploit the Fourth Crusade; and in the former,

as in the latter, Innocent had reluctantly to consent to the results

of the secular motives which had infected a spiritual enterprise. The

Albigensian Crusades, however, belong to French history; and it can

only be noted here that their ultimate result was the absorption of

the fertile lands, and the extinction of the peculiar civilization,

of southern France by the northern monarchy. (See the article

ALBIGENSES.)

[47] A canon of the third Lateran council (1179) forbade traffic with

the Saracens in munitions of war; and this canon had been renewed by

Innocent in the beginning of his pontificate.

[48] He had promised the pope, at his coronation in 1220, to begin

his Crusade in August 1221. But he declared himself exhausted by the

expenses of his coronation; and Honorius III. consented to defer his

Crusade until March 1222. The letter of the pope informing Pelagius

of this delay is dated the 20th of June: it would probably reach his

hands _after_ his departure from Damietta; and thus the Cardinal gave

the signal for the march, when, as he thought, the emperor's coming

was imminent.

[49] Joinville, ch. x.

[50] John of Brienne had only ruled in right of his wife Mary. On her

death (1212) John might be regarded as only ruling "by the courtesy

of the kingdom" until her daughter Isabella was married, when the

husband would succeed. That, at any rate, was the view Frederick II.

took.

[51] Amalric I. of Cyprus had done homage to Henry VI., from whom he

had received the title of king (1195).

[52] It may be argued that the Crusade against a revolted Christian

like Frederick II. was not misplaced, and that the pope had a true

sense of religious values when he attacked Frederick. The answer is

partly that men like St Louis _did_ think that the Crusade was

misplaced, and partly that Frederick was really attacked _not_ as a

revolted Christian, but as the would-be unifier of Italy, the enemy

of the states of the church.

[53] The following table of the Ayyubite rulers serves to illustrate

the text:--

Shadhy.

|

+----+----+

| |

Shirguh. Ayyub (both generals in the army of the Atabegs of Mosul).

|

+---------+---------------+

| |

Saladin Malik-al-Adil I.

+ 1193 + 1218.

|

+----------------+---+--------------+---------------------+

| | | |

Malik-al-Kamil, Malik-al-Muazzam, Malik-al-Ashraf, Malik-al-Salih Isma'il

Sultan of Egypt Sultan of Damascus ruler of Khelat, sultan of Damascus,

+ 1238. + 1227. and after 1227 1237-1244. From

| | of Damascus, him Damascus passed

| | + 1237. to Malik-al-Salih

| Malik-al-Nasir Ayyub of Egypt at

| of Kerak the battle of Gaza.

|

+--+--------------------+

| |

Malik-al-Adil II. Malik-al-Salih Najm

deposed 1240. al-din Ayyub, sultan

of Egypt, and after

1244 of Damascus,

+ 1249.

|

+-----------+

|

Turanshah, deposed 1250, and

succeeded by the Mameluke Aibek.

[54] Though Europe indulged in dreams of Mongol aid, the eventual

results of the extension of the Mongol Empire were prejudicial to the

Latin East. The sultans of Egypt were stirred to fresh activity by

the attacks of the Mongols; and as Syria became the battleground of

the two, the Latin principalities of Syria were fated to fall as the

prize of victory to one or other of the combatants.

[55] Of the four Latin principalities of the East, Edessa was the

first to fall, being extinguished between 1144 and 1150. Antioch fell

in 1268; Tripoli in 1289; and the kingdom itself may be said to end

with the capture of Acre, 1291.

[56] Michael Palaeologus had actually appealed to Louis IX. against

Charles of Anjou, who in 1270 had actively begun preparations for the

attack on Constantinople.

[57] The dream of a Crusade to Jerusalem survived de Mezieres; a

society which read "romaunts" of the Crusades, could not but dream

the dream. Henry V., whose father had fought with the Teutonic

knights on the Baltic, dreamed of a voyage to Jerusalem.

[58] The union of 1274, conceded by the Palaeologi at the council of

Lyons in order to defeat the plans of Charles of Anjou, had only been

temporary.

[59] Brehier, _L'Eglise el l'Orient_, p. 347.

[60] _Cambridge Modern History_, i. 11. It is perhaps worth remarking

that something of the old crusading spirit seems still to linger in

the movement of Russia towards Constantinople.

[61] While from this point of view the Crusades appear as a failure,

it must not be forgotten that elsewhere than in the East Crusades did

attain some success. A Crusade won for Christianity the coast of the

eastern Baltic (see TEUTONIC ORDER); and the centuries of the Spanish

Crusade ended in the conquest of the whole of Spain for Christianity.

[62] Authors like Heeren (_Versuch einer Entwickelung der Folgen der

Kreuzzuge_) and Michaud (in the last volume of his _Histoire des

croisades_) fall into the error of assigning all things to the

Crusades. Even Prutz, in his _Kulturgeschichte der Kreuzzuge_,

over-estimates the influence of the Crusades as a chapter in the

history of civilization. He depreciates unduly the Western

civilization of the early middle ages, and exalts the civilization of

the Arabs; and starting from these two premises, he concludes that

modern civilization is the offspring of the Crusades, which first

brought East and West together.

[63] It is difficult to decide how far Arabic models influenced

ecclesiastical architecture in the West as a result of the Crusades.

Greater freedom of moulding and the use of trefoil and cinquefoil may

be, but need not be, explained in this way. The pointed arch owes

nothing to the Arabs; it is already used in England in early Norman

work. Generally, one may say that Western architecture is independent

of the East.

[64] His somewhat legendary treatise, _De liberatione civitatum

Orientis_, was only composed about 1155.

[65] There is also an _Inventaire critique_ of these letters by the

comte de Riant (Paris, 1880).

[66] Von Sybel's view must be modified by that of Kugler, to which a

scholar like Hagenmeyer has to some extent given his adhesion (cf.

his edition of the _Gesta_, pp. 62-68). Hagenmeyer inclines to

believe in an original author, distinct from Albert the copyist; and

he thinks that this original author (whether or no he was present

during the Crusade) used the _Gesta_ and also Fulcher, though he had

probably also "_eigene Notizen und Aufzeichnungen_."

[67] See Pigonneau, _Le Cycle de la croisade_, &c. (Paris, 1877); and

Hagenmeyer, _Peter der Eremite_ (Leipzig, 1879).

[68] On the bibliography of the Second Crusade see Kugler, _Studien

zur Geschichte des zweiten Kreuzzuges_ (Stuttgart, 1866).

[69] Of these writers see Archer's _Crusade of Richard I._, Appendix

(in Nutt's series of Histories from Contemporary Writers).

[70] The bibliography of the Fourth Crusade is discussed in Klimke,

_Die Quellen zur Geschichte des vierten Kreuzzuges_ (Breslau, 1875).

CRUSENSTOLPE, MAGNUS JAKOB (1795-1865), Swedish historian, early became

famous both as a political and a historical writer. His first important

work was a _History of the Early Years of the Life of King Gustavus IV.

Adolphus_, which was followed by a series of monographs and by some

politico-historical novels, of which _The House of Holstein-Gottorp in

Sweden_ is considered the best. He obtained a great influence over King

Charles XIV. (Bernadotte), who during the years 1830-1833 gave him his

fullest confidence, and sanctioned the official character of

Crusenstolpe's newspaper _Faderneslandet_. In the last-mentioned year,

however, the historian suddenly became the king's bitterest enemy, and

used his acrid pen on all occasions in attacking him. In 1838 he was

condemned, for one of these angry utterances, to be imprisoned three

years in the castle of Waxholm. He continued his literary labours until

his death in 1865. Few Swedish writers have wielded so pure and so

incisive a style as Crusenstolpe, but his historical work is vitiated by

political and personal bias.

CRUSIUS, CHRISTIAN AUGUST (1715-1775), German philosopher and

theologian, was born on the 10th of January 1715 at Lenau near Merseburg

in Saxony. He was educated at Leipzig, and became professor of theology

there in 1750, and principal of the university in 1773. He died on the

18th of October 1775. Crusius first came into notice as an opponent of

the philosophy of Leibnitz and Wolff from the standpoint of religious

orthodoxy. He attacked it mainly on the score of the moral evils that

must flow from any system of determinism, and exerted himself in

particular to vindicate the freedom of the will. The most important

works of this period of his life are _Entwurf der nothwendigen

Vernunftwahrheiten_ (1745), and _Weg zur Gewissheit und Zuverlassigkeit

der menschlichen Erkenntniss_ (1747). Though diffusely written, and

neither brilliant nor profound, Crusius' philosophical books had a great

but short-lived popularity. His criticism of Wolff, which is generally

based on sound sense, had much influence upon Kant at the time when his

system was forming; and his ethical doctrines are mentioned with respect

in the _Kritik of Practical Reason_. Crusius's later life was devoted to

theology. In this capacity his sincere piety and amiable character

gained him great influence, and he led the party in the university which

became known as the "Crusianer" as opposed to the "Ernestianer," the

followers of J. A. Ernesti. The two professors adopted opposite methods

of exegesis. Ernesti wished to subject the Scripture to the same laws of

exposition as are applied to other ancient books; Crusius held firmly to

orthodox ecclesiastical tradition. Crusius's chief theological works are

_Hypomnemata ad theologiam propheticam_ (1764-1778), and _Kurzer Entwurf

der Moraltheologie_ (1772-1773). He sets his face against innovation in

such matters as the accepted authorship of canonical writings, verbal

inspiration, and the treatment of persons and events in the Old

Testament as types of the New. His views, unscholarly and uncritical as

they seem to us now, have had influence on later evangelical students of

the Old Testament, such as E. W. Hengstenberg and F. Delitzsch.

There is a full notice of Crusius in Ersch and Gruber's _Allgemeine

Encyclopadie_. Consult also J. E. Erdmann's _History of Philosophy_;

A. Marquardt, _Kant und Crusius_; and art. in Herzog-Hauck,

_Realencyklopadie_ (1898). (H. St.)

CRUSTACEA, a very large division of the animal kingdom, comprising the

familiar crabs, lobsters, crayfish, shrimps and prawns, the sandhoppers

and woodlice, the strangely modified barnacles and the minute

water-fleas. Besides these the group also includes a multitude of

related forms which, from their aquatic habits and generally

inconspicuous size, and from the fact that they are commonly neither

edible nor noxious, are little known except to naturalists and are

undistinguished by any popular names. Collectively, they are ranked as

one of the classes forming the sub-phylum ARTHROPODA, and their

distinguishing characters are discussed under that heading. It will be

sufficient here to define them as Arthropoda for the most part of

aquatic habits, having typically two pairs of antenniform appendages in

front of the mouth and at least three pairs of post-oral limbs acting as

jaws.

As a matter of fact, however, the range of structural variation within

the group is so wide, and the modifications due to parasitism and other

causes are so profound, that it is almost impossible to frame a

definition which shall be applicable to all the members of the class. In

certain parasites, for instance, the adults have lost every trace not

only of Crustacean but even of Arthropodous structure, and the only clue

to their zoological position is that afforded by the study of their

development. In point of size also the Crustacea vary within very wide

limits. Certain water-fleas (Cladocera) fall short of one-hundredth of

an inch in total length; the giant Japanese crab (_Macrocheira_) can

span over 10 ft. between its outstretched claws.

The habits of the Crustacea are no less diversified than their

structure. Most of them inhabit the sea, but representatives of all the

chief groups are found in fresh water (though the Cirripedia have hardly

gained a footing there), and this is the chief home of the primitive

Phyllopoda. A terrestrial habitat is less common, but the

widely-distributed land Isopoda or woodlice and the land-crabs of

tropical regions have solved the problem of adaptation to a subaerial

life.

Swimming is perhaps the commonest mode of locomotion, but numerous forms

have taken to creeping or walking, and the robber-crab (_Birgus latro_)

of the Indo-Pacific islands even climbs palm-trees. None has the power

of flight, though certain pelagic Copepoda are said to leap from the

surface of the sea like flying-fish. Apart from the numerous parasitic

forms, the only Crustacea which have adopted a strictly sedentary habit

of life are the Cirripedia, and here, as elsewhere, profound

modifications of structure have resulted, leading ultimately to a

partial assumption of the radial type of symmetry which is so often

associated with a sedentary life.

Many, perhaps the majority, of the Crustacea are omnivorous or

carrion-feeders, but many are actively predatory in their habits, and

are provided with more or less complex and efficient instruments for

capturing their prey, and there are also many plant-eaters. Besides the

sedentary Cirripedia, numbers of the smaller forms, especially among the

Entomostraca, subsist on floating particles of organic matter swept

within reach of the jaws by the movements of the other limbs.

Symbiotic association with other animals, in varying degrees of

interdependence, is frequent. Sometimes the one partner affords the

other merely a convenient means of transport, as in the case of the

barnacles which grow on, or of the gulf-weed crab which clings to, the

carapace of marine turtles. From this we may pass through various grades

of "commensalism," like that of the hermit-crab with its protective

anemones, to the cases of actual parasitism. The parasitic habit is most

common among the Copepoda and Isopoda, where it leads to complex

modifications of structure and life-history. Perhaps the most complete

degeneration is found in the Rhizocephala, which are parasitic on other

Crustacea. In these the adult consists of a simple saccular body

containing the reproductive organs and attached by root-like filaments

which ramify throughout the body of the host and serve for the

absorption of nourishment (fig. 1).

Many of the larger species of Crustacea are used as food by man, the

most valuable being the lobster, which is caught in large quantities on

both sides of the North Atlantic. Perhaps the most important of all

Crustacea, however, with respect to the part which they play in the

economy of nature, are the minute pelagic Copepoda, of which

incalculable myriads form an important constituent of the "plankton" in

all the seas of the globe. It is on the plankton that a great part of

the higher animal life of the sea ultimately depends for food. The

Copepoda live upon the diatoms and other important microscopic vegetable

life at the surface of the sea, and in their turn serve as food for

fishes and other larger forms and thus, indirectly, for man himself.

[Illustration: FIG. 1.

A, Group of _Peltogaster socialis_ on the abdomen of a small

hermit-crab; in one of them the fasciculately ramified roots, r, in

the liver of the crab are shown (Fritz Muller).

B, Young of _Sacculina purpurea_ with its roots. (Fritz Muller.)]

_Historical Sketch._--In common with most branches of natural history,

the science of Carcinology may be traced back to its beginnings in the

writings of Aristotle. It received additions of varying importance at

the hands of medieval and later naturalists, and first began to assume

systematic form under the influence of Linnaeus. The application of the

morphological method to the Crustacea may perhaps be dated from the work

of J. C. Fabricius towards the end of the 18th century.

In the first quarter of the 19th century important advances in

classification were made by P. A. Latreille, W. E. Leach and others, and

J. Vaughan Thompson demonstrated the existence of metamorphosis in the

development of the higher Crustacea. A new epoch may be said to begin

with H. Milne-Edwards' classical _Histoire naturelle des crustaces_

(1834-1840). It is noteworthy that even at this late date the Cirripedia

(Thyrostraca) were still excluded from the Crustacea, though Darwin's

Monograph (1851-1854) was soon to make them known with a wealth of

anatomical and systematic detail such as was available, at that time,

for few other groups of Crustacea. About the same period three authors

call for special mention, W. de Haan, J. D. Dana and H. Kroyer. The new

impulse given to biological research by the publication of the _Origin

of Species_ bore fruit in Fritz Muller's _Fur Darwin_, in which an

attempt was made to reconstruct the phylogenetic history of the class.

The same line of work was followed in the long series of important

memoirs from the pen of K. F. W. Claus, and noteworthy contributions

were made, among many others, by A. Dohrn, Ray Lankester and Huxley. In

more recent years the long and constantly increasing list of writers on

Crustacea contains no name more honoured than that of the veteran G. O.

Sars of Christiania.

[Illustration: FIG. 2.--Abdominal Somite of a Lobster, separated and

viewed from in front. t, tergum; s, sternum; pl, pleuron.]

_Morphology._

_External Structure: Body._--As in all Arthropoda the body consists of

a series of segments or somites which may be free or more or less

coalesced together. In its simplest form the exoskeleton of a typical

somite is a ring of chitin defined from the rings in front and behind

by areas of thinner integument forming moveable joints, and having a

pair of appendages articulated to its ventral surface on either side

of the middle line. Frequently, however, this exoskeletal somite may

be differentiated into various regions. A dorsal and a ventral plate

are often distinguished, known respectively as the tergum and the

sternum, and the tergum may overhang the insertion of the limb on each

side as a free plate called the pleuron. The name epimeron is

sometimes applied to what is here called the pleuron, but the word has

been used in widely different senses and it seems better to abandon

it. The typical form of a somite is well seen, for example, in the

segments which make up the abdomen or "tail" of a lobster or crayfish

(fig. 2). The posterior terminal segment of the body, on which the

opening of the anus is situated, never bears appendages. The nature of

this segment, which is known as the "anal segment" or telson (fig. 3,

T), has been much discussed, some authorities holding that it is a

true somite, homologous with those which precede it. Others have

regarded it as representing the fusion of a number of somites, and

others again as a "median appendage" or as a pair of appendages fused.

Its morphological nature, however, is clearly shown by its

development. In the larval development of the more primitive

Crustacea, the number of somites, at first small, increases by the

successive appearance of new somites between the last-formed somite

and the terminal region which bears the anus. The "growing point" of

the trunk is, in fact, situated in front of this region, and, when the

full number of somites has been reached, the unsegmented part

remaining forms the telson of the adult.

[Illustration: FIG. 3.--The Separated Somites and Appendages of the

Common Lobster (_Homarus gammarus_).

C, carapace covering the cephalothorax.

Ab, abdominal somites.

T, telson, having the uropods or appendages of the last abdominal

somite spread out on either side of it, forming the "tail-fan."

l, labrum, or upper lip.

m, metastoma, or lower lip.

1, eyes.

2, antennule (the arrow points to the opening of the so-called

auditory organ).

3, antenna.

4, mandible.

5, maxillula (or first maxilla).

6, maxilla (second maxilla).

7-9, first, second and third maxillipeds.

ex, exopodite.

ep, epipodite.

g, gill.

10, sixth thoracic limb (second walking-leg) of female.

11, last thoracic limb of male. In 10 and 11 the arrows indicate the

genital apertures.

13, sterna of the thoracic somites, from within.

14, third abdominal somite, with appendages or "swimmerets."]

In no Crustacean, however, do all the somites of the body remain

distinct. Coalescence, or suppression of segmentation ("lipomerism"),

may involve more or less extensive regions. This is especially the

case in the anterior part of the body, where, in correlation with the

"adaptational shifting of the oral aperture" (see ARTHROPODA), a

varying number of somites unite to form the "cephalon" or head. Apart

from the possible existence of an ocular somite corresponding to the

eyes (the morphological nature of which is discussed below), the

smallest number of head-somites so united in any Crustacean is five.

Even where a large number of the somites have fused, there is

generally a marked change in the character of the appendages after the

fifth pair, and since the integumental fold which forms the carapace

seems to originate from this point, it is usual to take the fifth

somite as the morphological limit of the cephalon throughout the

class. It is quite probable, however, that in the primitive ancestors

of existing Crustacea a still smaller number of somites formed the

head. The three pairs of appendages present in the "nauplius" larva

show certain peculiarities of structure and development which seem to

place them in a different category from the other limbs, and there is

some ground for regarding the three corresponding somites as

constituting a "primary cephalon." For practical purposes, however, it

is convenient to include the two following somites also as cephalic.

[Illustration: FIG. 4.--Diagram of an Amphipod. (After Spence Bate and

Westwood.)

C, cephalon.

Th, thorax. (Only seven of the eight thoracic somites are visible,

the first being fused with the cephalon.)

Ab, abdomen.

The numbers appended to the somites do not correspond to the

enumeration adopted in the text. 21 is the telson.]

A remarkable feature found only in the Stomatopoda is the reappearance

of segmentation in the anterior part of the cephalic region. Whether

the movably articulated segments which bear the eye-stalks and the

antennules in this aberrant group correspond to the primitive head

somites or not, their distinctness is certainly a secondarily acquired

character, for it is not found in the larvae, nor in any of the more

primitive groups of Malacostraca.

The body proper is usually divisible into two regions to which the

names _thorax_ and _abdomen_ are applied. Throughout the whole of the

Malacostraca the thorax consists of eight and the abdomen of six

somites (fig. 4), and the two regions are sharply distinguished by the

character of their appendages. In the various groups of the

Entomostraca, on the other hand, the terms thorax and abdomen, though

conveniently employed for purposes of systematic description, do not

imply any homology with the regions so named in the Malacostraca.

Sometimes they are applied, as in the Copepoda, to the limb-bearing

and limbless regions of the trunk, while in other cases, as in the

Phyllopoda, they denote, respectively, the regions in front of and

behind the genital apertures.

[Illustration: FIG. 5.--Phyllopoda and Phyllocarida.

1, _Ceratiocaris papilio_, U. Silurian, Lanark.

2, _Nebalia bipes_(one side of carapace removed).

3, _Lepidurus Angassi_: a, dorsal aspect; b, ventral aspect of head

showing the labrum and mouth-parts.

4, larva of _Apus cancriformis_.

5, _Branchipus stagnalis_: a, adult female; b, first larval stage

(Nauplius); c, second larval stage.

6, Nauplius of _Artemia salina_.]

A character which recurs in the most diverse groups of the Crustacea,

and which is probably to be regarded as a primitive attribute of the

class, is the possession of a carapace or shell, arising as a dorsal

fold of the integument from the posterior margin of the head-region.

In its most primitive form, as seen in the _Apodidae_ (fig. 5, 3) and

in _Nebalia_ (fig. 5, 2), this shell-fold remains free from the trunk,

which it envelops more or less completely. It may assume the form of a

bivalve shell entirely enclosing the body and limbs, as in many

Phyllopoda (fig. 6) and in the Ostracoda. In the Cirripedia it forms

a fleshy "mantle" strengthened by shelly plates or valves which may

assume a very complex structure. In many cases, however, the

shell-fold coalesces with some of the succeeding somites. In the

Decapoda (fig. 3), this coalescence affects only the dorsal region of

the thoracic somites, and the lateral portions of the carapace

overhang on each side, enclosing a pair of chambers within which lie

the gills. The arrangement is similar in Schizopoda and Stomatopoda

(fig. 7), except that the coalescence does not usually involve the

posterior thoracic somites, several of which remain free, though they

may be overlapped by the carapace.

[Illustration: From Morse's _Zoology_.

FIG. 6.--_Estheria_, sp.; D from Dubuque, Iowa; (e) the eye. L from

Lynn, Massachusetts (nat. size). S presents a highly magnified section

of one of the valves to show the successive moults. B an enlarged

portion of the edge of the shell along the back, showing the overlap

of each growth.]

In the Isopoda and Amphipoda, where, as a rule, all the thoracic

somites except the first are distinct (fig. 4), there seems at first

sight to be no shell-fold. A comparison with the related Tanaidacea

(fig. 8) and Cumacea (or Sympoda), however, leads to the conclusion

that the coalescence of the first thoracic somite with the cephalon

really involves a vestigial shell-fold, and, indeed, traces of this

are said to be observed in the embryonic development of some Isopoda.

It seems likely that a similar explanation is to be applied to the

coalescence of one or two trunk-somites with the head in the Copepoda,

and, if this be so, the only Crustacea remaining in which no trace of

a shell-fold is found in the adult are the Anostracous Phyllopoda such

as Branchipus (fig. 5, 5).

[Illustration: FIG. 7.--_Squilla mantis_ (Stomatopoda), showing the

last four thoracic (leg-bearing) somites free from the carapace.]

_General Morphology of Appendages._--Amid the great variety of forms

assumed by the appendages of the Crustacea, it is possible to trace,

more or less plainly, the modifications of a fundamental type

consisting of a peduncle, the protopodite, bearing two branches, the

endopodite and exopodite. This simple biramous form is shown in the

swimming-feet of the Copepoda and Branchiura, the "cirri" of the

Cirripedia, and the abdominal appendages of the Malacostraca (fig. 3,

14). It is also found in the earliest and most primitive form of

larva, known as the _Nauplius_. As a rule the protopodite is composed

of two segments, though one may be reduced or suppressed and

occasionally three may be present. In many cases, one of the branches,

generally the endopodite, is more strongly developed than the other.

Thus, in the thoracic limbs of the Malacostraca, the endopodite

generally forms a walking-leg while the exopodite becomes a

swimming-branch or may disappear altogether. Very often the basal

segment of the protopodite bears, on the outer side, a lamellar

appendage (more rarely, two), the epipodite, which may function as a

gill. In the appendages near the mouth one or both of the protopodal

segments may bear inwardly-turned processes, assisting in mastication

and known as gnathobases. The frequent occurrence of epipodites and

gnathobases tends to show that the primitive type of appendage was

more complex than the simple biramous limb, and some authorities have

regarded the leaf-like appendages of the Phyllopoda as nearer the

original form from which the various modifications found in other

groups have been derived. In a Phyllopod such as _Apus_ the limbs of

the trunk consist of a flattened, unsegmented or obscurely segmented

axis or corm having a series of lobes or processes known as endites

and exites on its inner and outer margins respectively. In all the

Phyllopoda the number of endites is six, and the proximal one is more

or less distinctly specialized as a gnathobase, working against its

fellow of the opposite side in seizing food and transferring it to the

mouth. The Phyllopoda are the only Crustacea in which distinct and

functional gnathobasic processes are found on appendages far removed

from the mouth. The two distal endites are regarded as corresponding

to the endopodite and exopodite of the higher Crustacea, the axis or

corm of the Phyllopod limb representing the protopodite. The number of

exites is less constant, but, in _Apus_, two are present, the proximal

branchial in function and the distal forming a stiffer plate which

probably aids in swimming. It is not altogether easy to recognize the

homologies of the endites and exites even within the order Phyllopoda,

and the identification of the two distal endites as corresponding to

the endopodite and exopodite of higher Crustacea is not free from

difficulty. It is highly probable, however, that the biramous limb is

a simplification of a more complex primitive type, to which the

Phyllopod limb is a more or less close approximation.

[Illustration: FIG. 8.--_Tanais dubius_ (?) Kr. [female], showing the

orifice of entrance (x) into the cavity overarched by the carapace in

which an appendage of the maxilliped (f) plays. On four feet (i, k, l,

m) are the rudiments of the lamellae which subsequently form the

brood-cavity. (Fritz Muller.)]

[Illustration: FIG. 9.--A, _Balanus_ (young), side view with cirri

protruded. B, Upper surface of same; valves closed. C, Highly

magnified view of one of the cirri. (Morse.)]

The modifications which this original type undergoes are usually more

or less plainly correlated with the functions which the appendages

have to discharge. Thus, when acting as swimming organs, the

appendages, or their rami, are more or less flattened, or oar-like,

and often have the margins fringed with long plumose hairs. When used

for walking, one of the rami, usually the inner, is stout and

cylindrical, terminating in a claw, and having the segments united by

definite hinge-joints. The jaws have the gnathobasic endites developed

at the expense of the rest of the limb, the endopodite and exopodite

persisting only as sensory "palps" or disappearing altogether. When

specialized as bearers of sensory (olfactory or tactile) organs, the

rami are generally elongated, many-jointed and flagelliform. This

modification is usually only found in the antennules and antennae, but

it may exceptionally be found in the appendages of the trunk, as, for

instance, in the thoracic legs of some Decapods (e.g.

_Mastigocheirus_). Very often one or other of the appendages may be

modified for prehension, the seizing of prey or the holding of a mate.

In this case, the claw-like terminal segment may be simply flexed

against the preceding in the same way as the blade of a penknife shuts

up against the handle. The penultimate segment is often broadened, so

that the terminal claw shuts against a transverse edge (fig. 4), or,

finally, the penultimate segment may be produced into a thumb-like

process opposed to the movable terminal segment or finger, forming a

perfect chela or forceps, as, for instance, in the large claws of a

crab or lobster. This chelate condition may be assumed by almost any

of the appendages, and sometimes it appears in different appendages in

closely related forms, so that no very great phylogenetic importance

can in most cases be attached to it. A peculiar modification is found

in the trunk-limbs of the Cirripedia (fig. 9), in which both rami are

multiarticulate and filiform and fringed with long bristles. When

protruded from the opening of the shell these "cirri" are spread out

to form a casting-net for the capture of minute floating prey.

Gills or branchiae may be developed by parts of an appendage becoming

thin-walled and vascular and either expanded into a thin lamella or

ramified. Some of the special modifications of branchiae are referred

to below.

_Special Morphology of Appendages._--In many Crustacea the eyes are

borne on stalks which are movably articulated with the head and which

may be divided into two or three segments. The view is commonly held

that these eye-stalks are really limbs, homologous with the other

appendages. In spite of much discussion, however, it cannot be said

that this point has been finally settled. The evidence of embryology

is decidedly against the view that the eye-stalks are limbs. They are

absent in the earliest and most primitive larval forms (nauplius),

and appear only late in the course of development, after many of the

trunk-limbs are fully formed. In the development of the Phyllopod

_Branchipus_, the eyes are at first sessile, and the lateral lobes of

the head on which they are set grow out and become movably

articulated, forming the peduncles. The most important evidence in

favour of their appendicular nature is afforded by the phenomena of

regeneration. When the eye-stalk is removed from a living lobster or

prawn, it is found that under certain conditions a many-jointed

appendage like the flagellum of an antennule or antenna may grow in

its place. It is open to question, however, how far the evidence from

such "heteromorphic regeneration" can be regarded as conclusive on the

points of homology. The fact that in certain rare cases among insects

a leg may apparently be replaced by a wing tends to show that under

exceptional conditions similar forms may be assumed by non-homologous

parts.

The antennules (or first antennae) are almost universally regarded as

true appendages, though they differ from all the other appendages in

the fact that they are always innervated from the "brain" (or preoral

ganglia), and that they are uniramous in the nauplius larva and in all

the Entomostracan orders. As regards their innervation an apparent

exception is found in the case of _Apus_, where the nerves to the

antennules arise, behind the brain, from the oesophageal commissures,

but this is, no doubt, a secondary condition, and the nerve-fibres

have been traced forwards to centres within the brain. In the

Malacostraca, the antennules are often biramous, but there is

considerable doubt as to whether the two branches represent the

endopodite and exopodite of the other limbs, and three branches are

found in the Stomatopoda and in some Caridea. In the great majority of

Crustacea the antennules are purely sensory in function and carry

numerous "olfactory" hairs. They may, however, be natatory as in many

Ostracoda and Copepoda, or prehensile, as in some Copepoda. The most

peculiar modification, perhaps, is that found in the Cirripedia

(Thyrostraca), in the larvae of which the antennules develop into

organs of attachment, bearing the openings of the cement-glands, and

becoming, in the adult, involved in the attachment of the animal to

its support.

The antennae (second antennae) are of special interest on account of

the clear evidence that, although preoral in position in all adult

Crustacea, they were originally postoral appendages. In the nauplius

larva they lie rather at the sides than in front of the mouth, and

their basal portion carries a hook-like masticatory process which

assists the similar processes of the mandibles in seizing food. In the

primitive Phyllopoda, and less distinctly in some other orders, the

nerves supplying the antennae arise, not from the brain, but from the

circum-oesophageal commissures, and even in those cases where the

nerves and the ganglia in which they are rooted have been moved

forwards to the brain, the transverse commissure of the ganglia can

still be traced, running behind the oesophagus.

The functions of the antennae are more varied than is the case with

the antennules. In many Entomostraca (Phyllopoda, Cladocera,

Ostracoda, Copepoda) they are important, and sometimes the only,

organs of locomotion. In some male Phyllopoda they form complex

"claspers" for holding the female. They are frequently organs of

attachment in parasitic Copepoda, and they may be completely pediform

in the Ostracoda. In the Malacostraca they are chiefly sensory, the

endopodite forming a long flagellum, while the exopodite may form a

lamellar "scale," probably useful as a balancer in swimming, or may

disappear altogether. A very curious function sometimes discharged by

the antennules or antennae of Decapods is that of forming a

respiratory siphon in sand-burrowing species.

The mandibles, like the antennae, have, in the nauplius, the form of

biramous swimming limbs, with a masticatory process originating from

the proximal part of the protopodite. This form is retained, with

little alteration in some adult Copepoda, where the biramous "palp"

still aids in locomotion. A somewhat similar structure is found also

in some Ostracoda. In most cases, however, the palp loses its

exopodite and it often disappears altogether, while the coxal segment

forms the body of the mandible, with a masticatory edge variously

armed with teeth and spines. In a few Ostracoda, by a rare exception,

the masticatory process is reduced or suppressed, and the palp alone

remains, forming a pediform appendage used in locomotion as well as in

the prehension of food. In parasitic blood-sucking forms the mandibles

often have the shape of piercing stylets, and are enclosed in a

tubular proboscis formed by the union of the upper lip (labrum) with

the lower lip (hypostome or paragnatha).

The maxillulae and maxillae (or, as they are often termed, first and

second maxillae) are nearly always flattened leaf-like appendages,

having gnathobasic lobes or endites borne by the segments of the

protopodite. The endopodite, when present, is unsegmented or composed

of few segments and forms the "palp," and outwardly-directed lobes

representing the exopodite and epipodites may also be present. These

limbs undergo great modification in the different groups. The

maxillulae are sometimes closely connected with the "paragnatha" or

lobes of the lower lip, when these are present, and it has been

suggested that the paragnatha are really the basal endites which have

become partly separated from the rest of the appendage.

The limbs of the post-cephalic series show little differentiation

among themselves in many Entomostraca. In the Phyllopoda they are for

the most part all alike, though one or two of the anterior pairs may

be specialized as sensory (_Apus_) or grasping (_Estheriidae_) organs.

In the Cirripedia (Thyrostraca) the six pairs of biramous cirriform

limbs differ only slightly from each other, and in many Copepoda this

is also the case. In other Entomostraca considerable differentiation

may take place, but the series is never divided into definite

"tagmata" or groups of similarly modified appendages. It is highly

characteristic of the Malacostraca, however, that the trunk-limbs are

divided into two sharply defined tagmata corresponding to the thoracic

and abdominal regions respectively, the limit between the two being

marked by the position of the male genital openings. The thoracic

limbs have the endopodites converted, as a rule, into more or less

efficient walking-legs, and the exopodites are often lost, while the

abdominal limbs more generally preserve the biramous form and are, in

the more primitive types, natatory. These tagmata may again be

subdivided into groups preserving a more or less marked individuality.

For example, in the Amphipoda (fig. 4) the abdominal appendages are

constantly divided into an anterior group of three natatory

"swimmerets" and a posterior group of three limbs used chiefly in

jumping or in burrowing. In nearly all Malacostraca the last pair of

abdominal appendages (uropods) differ from the others, and in the more

primitive groups they form, with the telson, a lamellar "tail-fan"

(fig. 3, T), used in springing backwards through the water. In the

thoracic series it is usual for one or more of the anterior pairs to

be pressed into the service of the mouth, forming "foot-jaws" or

maxillipeds. In the Decapoda three pairs are thus modified, and in the

Tanaidacea, Isopoda and Amphipoda only one. In the Schizopoda and

Cumacea the line of division is less sharp, and the varying number of

so-called maxillipeds recognized by different authors gives rise to

some confusion of terminology in systematic literature.

_Gills._--In many of the smaller Entomostraca (Copepoda and most

Ostracoda) no special gills are present, and respiration is carried on

by the general surface of the body and limbs. When present, the

branchiae are generally differentiations of parts of the appendages,

most often the epipodites, as in the Phyllopoda. In the Cirripedia,

however, they are vascular processes from the inner surface of the

mantle or shell-fold, and in some Ostracoda they are outgrowths from

the sides of the body. In the primitive Malacostraca the gills were

probably, as in the Phyllopoda and in _Nebalia_, the modified

epipodites of the thoracic limbs, and this is the condition found in

some Schizopoda. In the Cumacea and Tanaidacea only the first thoracic

limb has a branchial epipodite. In the Amphipoda, the gills though

arising from the inner side of the bases of the thoracic legs are

probably also epipodial in nature. In the Isopoda the respiratory

function has been taken over by the abdominal appendages, both rami or

only the inner becoming thin or flattened. In the Decapoda the

branchial system is more complex. The gills are inserted at the base

of the thoracic limbs, and lie within a pair of branchial chambers

covered by the carapace. Three series are distinguished,

_podobranchiae_, attached to the proximal segments of the appendages,

_pleurobranchiae_, springing from the body-wall, and an intermediate

series, _arthrobranchiae_, inserted on the articular membrane of the

joint between the limb and the body. The podobranchiae are clearly

epipodites, or, more correctly, parts of the epipodites, and it is

probable that the arthro- and pleurobranchiae are also epipodial in

origin and have migrated from the proximal segment of the limbs on to

the adjacent body-wall.

Adaptations for aerial respiration are found in some of the

land-crabs, where the lining membrane of the gill-chamber is beset

with vascular papillae and acts as a lung. In some of the terrestrial

Isopoda or woodlice (Oniscoidea) the abdominal appendages have

ramified tubular invaginations of the integument, filled with air and

resembling the tracheae of insects.

_Internal Structure: Alimentary System._--In almost all Crustacea the

food-canal runs straight through the body, except at its anterior end,

where it curves downwards to the ventrally-placed mouth. In a few

cases its course is slightly sinuous or twisted, but the only cases in

which it is actually coiled upon itself are found in the Cladocera of

the family _Lynceidae_ (_Alonidae_) and in a single

recently-discovered genus of Cumacea (Sympoda). As in all Arthropoda,

it is composed of three divisions, a fore-gut or stomodaeum,

ectodermal in origin and lined by an inturning of the chitinous

cuticle, a mid-gut formed by endoderm and without a cuticular lining,

and a hind-gut or proctodaeum, which, like the fore-gut, is ectodermal

and is lined by cuticle. The relative proportions of these three

divisions vary considerably, and the extreme abbreviation of the

mid-gut found in the common crayfish (_Astacus_) is by no means

typical of the class. Even in the closely-related lobster (_Homarus_)

the mid-gut may be 2 or 3 in. long.

In a few Entomostraca (some Phyllopoda and Ostracoda) the chitinous

lining of the fore-gut develops spines and hairs which help to

triturate and strain the food, and among the Ostracods there is

occasionally (_Bairdia_) a more elaborate armature of toothed plates

moved by muscles. It is among the Malacostraca, however, and

especially in the Decapoda, that the "gastric mill" reaches its

greatest perfection. In most Decapods the "stomach" or dilated portion

of the fore-gut is divided into two chambers, a large anterior

"cardiac" and a smaller posterior "pyloric." In the narrow opening

between these, three teeth (fig. 10) are set, one dorsally and one on

each side. These teeth are connected with a framework of movably

articulated ossicles developed as thickened and calcified portions of

the lining cuticle of the stomach and moved by special muscles in such

a way as to bring the three teeth together in the middle line. The

walls of the pyloric chamber bear a series of pads and ridges beset

with hairs and so disposed as to form a straining apparatus.

The mid-gut is essentially the digestive and absorptive region of the

alimentary canal, and its surface is, in most cases, increased by

pouch-like or tubular outgrowths which not only serve as glands for

the secretion of the digestive juices, but may also become filled by

the more fluid portion of the partially digested food and facilitate

its absorption. These outgrowths vary much in their arrangement in the

different groups. Most commonly there is a pair of lateral caeca,

which may be more or less ramified and may form a massive

"hepato-pancreas" or "liver."

[Illustration: FIG. 10.--Gastric Teeth of Crab and Lobster.

1a, Stomach of common crab, _Cancer pagurus_, laid open, showing b,

b, b, some of the calcareous plates inserted in its muscular coat;

g, g, the lateral teeth, which when in use are brought in contact

with the sides of the median tooth m; c, c, the muscular coat.

1b' and 1b", The gastric teeth enlarged to show their grinding

surfaces.

2, Gastric teeth of common lobster, _Homarus vulgaris_.

3a and 3b, Two crustacean teeth (of _Dithyrocaris_) from the

Carboniferous series of Renfrewshire (these, however, may be the

toothed edges of the mandibles).]

The whole length of the alimentary canal is provided, as a rule, with

muscular fibres, both circular and longitudinal, running in its walls,

and, in addition, there may be muscle-bands running between the gut

and the body-wall. In the region of the oesophagus these muscles are

more strongly developed to perform the movements of deglutition, and,

where a gastric mill is present, both intrinsic and extrinsic muscles

co-operate in producing the movements of its various parts. The

hind-gut is also provided with sphincter and dilator muscles, and

these may produce rhythmic expansion and contraction, causing an

inflow and outflow of water through the anus, which has been supposed

to aid in respiration.

In the parasitic Rhizocephala and in a few Copepoda (_Monstrillidae_)

the alimentary canal is absent or vestigial throughout life.

_Circulatory System._--As in the other Arthropoda, the circulatory

system in Crustacea is largely lacunar, the blood flowing in spaces or

channels without definite walls. These spaces make up the apparent

body-cavity, the true body-cavity or coelom having been, for the most

part, obliterated by the great expansion of the blood-containing

spaces. The heart is of the usual Arthropodous type, lying in a more

or less well-defined pericardial blood-sinus, with which it

communicates by valvular openings or ostia. In the details of the

system, however, great differences exist within the limits of the

class. There is every reason to believe that, in the primitive

Arthropoda, the heart was tubular in form, extending the whole length

of the body, and having a pair of ostia in each somite. This

arrangement is retained in some of the Phyllopoda, but even in that

group a progressive abbreviation of the heart, with a diminution in

the number of the ostia, can be traced, leading to the condition found

in the closely related Cladocera, where the heart is a subglobular

sac, with only a single pair of ostia. In the Malacostraca, an

elongated heart with numerous segmentally arranged ostia is found only

in the aberrant group of Stomatopoda and in the transitional

Phyllocarida. In the other Malacostraca the heart is generally

abbreviated, and even where, as in the Amphipoda, it is elongated and

tubular, the ostia are restricted in number, three pairs only being

usually present. In many Entomostraca the heart is absent, and it is

impossible to speak of a "circulation" in the proper sense of the

term, the blood being merely driven hither and thither by the

movements of the body and limbs and of the alimentary canal.

A very remarkable condition of the blood-system, unique, as far as is

yet known among the Arthropoda, is found in a few genera of parasitic

Copepoda (_Lernanthropus_, _Mytilicola_). In these there is a closed

system of vessels, not communicating with the body-cavity, and

containing a coloured fluid. There is no heart. The morphological

nature of this system is unknown.

_Excretory System._--The most important excretory or renal organs of

the Crustacea are two pairs of glands lying at the base of the

antennae and of the second maxillae respectively. The two are probably

never functional together in the same animal, though one may replace

the other in the course of development. Thus, in the Phyllopoda, the

antennal gland develops early and is functional during a great part of

the larval life, but it ultimately atrophies, and in the adult (as in

most Entomostraca) the maxillary gland is the functional excretory

organ. In the Decapoda, where the antennal gland alone is

well-developed in the adult, the maxillary gland sometimes precedes it

in the larva. The structure of both glands is essentially the same.

There is a more or less convoluted tube with glandular walls connected

internally with a closed "end-sac" and opening to the exterior by

means of a thin-walled duct. Development shows that the glandular tube

is mesoblastic in origin and is of the nature of a coelomoduct, while

the end-sac is to be regarded as a vestigial portion of the coelom. In

the Branchiopoda the maxillary gland is lodged in the thickness of the

shell-fold (when this is present), and, from this circumstance, it

often receives the somewhat misleading name of "shell-gland." In the

Decapoda the antennal gland is largely developed and is known as the

"green gland." The external duct of this gland is often dilated into a

bladder, and may sometimes send out diverticula, forming a complex

system of sinuses ramifying through the body. The green gland and the

structures associated with it in Decapods were at one time regarded as

constituting an auditory apparatus.

In addition to these two pairs of glands, which are in all probability

the survivors of a series of segmentally arranged coelomoducts present

in the primitive Arthropoda, other excretory organs have been

described in various Crustacea. Although the excretory function of

these has been demonstrated by physiological methods, however, their

morphological relations are not clear. In some cases they consist of

masses of mesodermal cells, within which the excretory products appear

to be stored up instead of being expelled from the body.

_Nervous System._--The central nervous system is constructed on the

same general plan as in the other Arthropoda, consisting of a

supra-oesophageal ganglionic mass or brain, united by

circum-oesophageal connectives with a double ventral chain of

segmentally arranged ganglia. In the primitive Phyllopoda the ventral

chain retains the ladder-like arrangement found in some Annelids and

lower worms, the two halves being widely separated and the pairs of

ganglia connected together across the middle line by double transverse

commissures. In the higher groups the two halves of the chain are more

or less closely approximated and coalesced, and, in addition, a

concentration of the ganglia in a longitudinal direction takes place,

leading ultimately, in many cases, to the formation of an unsegmented

ganglionic mass representing the whole of the ventral chain. This is

seen, for example, in the Brachyura among the Decapoda. The brain, or

supra-oesophageal ganglion, shows various degrees of complexity. In

the Phyllopoda it consists mainly of two pairs of ganglionic centres,

giving origin respectively to the optic and antennular nerves. The

centres for the antennal nerves form ganglionic swellings on the

oesophageal connectives. In the higher forms, as already mentioned,

the antennal ganglia have become shifted forwards and coalesced with

the brain. In the higher Decapoda, numerous additional centres are

developed in the brain and its structure becomes extremely complex.

_Eyes._--The eyes of Crustacea are of two kinds, the unpaired, median

or "nauplius" eye, and the paired compound eyes. The former is

generally present in the earliest larval stages (nauplius), and in

some Entomostraca (e.g. Copepoda) it forms the sole organ of vision in

the adult. In the Malacostraca it is absent in the adult, or persists

only in a vestigial condition, as in some Decapoda and Schizopoda. It

is typically tripartite, consisting of three cup-shaped masses of

pigment, the cavity of each cup being filled with columnar retinal

cells. At their inner ends (towards the pigment) these cells contain

rod-like structures, while their outer ends are connected with the

nerve-fibres. In some cases three separate nerves arise from the front

of the brain, one going to each of the three divisions of the eye. In

the Copepoda the median eye may undergo considerable elaboration, and

refracting lenses and other accessory structures may be developed in

connexion with it.

The compound eyes are very similar in the details of their structure

(see ARTHROPODA) to those of insects (Hexapoda). They consist of a

varying number of ommatidia or visual elements, covered by a

transparent region of the external cuticle forming the cornea. In most

cases this cornea is divided into lenticular facets corresponding to

the underlying ommatidia.

As has been already stated, the compound eyes are often set on movable

peduncles. It is probable that this is the primitive condition from

which the sessile eyes of other forms have been derived. In the

Malacostraca the sessile eyed groups are certainly less primitive than

some of those with stalked eyes, and among the Entomostraca also there

is some evidence pointing in the same direction.

Although typically paired, the compound eyes may occasionally coalesce

in the middle line into a single organ. This is the case in the

Cladocera, the Cumacea and a few Amphipoda.

Mention should also be made of the partial or complete atrophy of the

eyes in many Crustacea which live in darkness, either in the deep sea

or in subterranean habitats. In these cases the peduncles may persist

and may even be modified into spinous organs of defence.

_Other Sense-Organs._--As in Arthropoda, the hairs or setae on the

surface of the body are important organs of sense and are variously

modified for special sensory functions. Many, perhaps all, of them

are tactile. They are movably articulated at the base where they are

inserted in pits formed by a thinning away of the cuticle, and each is

supplied by a nerve-fibril. When feathered or provided with secondary

barbs the setae will respond to movements or vibrations in the

surrounding water, and have been supposed to have an auditory

function. In certain divisions of the Malacostraca more specialized

organs are found which have been regarded as auditory. In the majority

of the Decapoda there is a saccular invagination of the integument in

the basal segment of the antennular peduncle having on its inner

surface "auditory" setae of the type just described. The sac is open

to the exterior in most of the Macrura, but completely closed in the

Brachyura. In the former case it contains numerous grains of sand

which are introduced by the animal itself after each moult and which

are supposed to act as otoliths. Where the sac is completely closed it

generally contains no solid particles, but in a few Macrura a single

otolith secreted by the walls of the sac is present. In the _Mysidae_

among the Schizopoda a pair of similar otocysts are found in the

endopodites of the last pair of appendages (uropods). These contain

each a single concretionary otolith.

Recent observations, however, make it very doubtful whether aquatic

Crustacea can hear at all, in the proper sense of the term, and it has

been shown that one function, at least, of the so-called otocysts is

connected with the equilibration of the body. They are more properly

termed statocysts.

Another modification of sensory setae is supposed to be associated

with the sense of smell. In nearly all Crustacea the antennules and

often also the antennae bear groups of hair-like filaments in which

the chitinous cuticle is extremely delicate and which do not taper to

a point but end bluntly. These are known as olfactory filaments or

aesthetascs. They are very often more strongly developed in the male

sex, and are supposed to guide the males in pursuit of the females.

_Glands._--In addition to the digestive and excretory glands already

mentioned, various glandular structures occur in the different groups

of Crustacea. The most important of these belong to the category of

dermal glands, and may be scattered over the surface of the body and

limbs, or grouped at certain points for the discharge of special

functions. Such glands occurring on the upper and lower lips or on the

walls of the oesophagus have been regarded as salivary. In some

Amphipoda the secretion of glands on the body and limbs is used in the

construction of tubular cases in which the animals live. In some

freshwater Copepoda the secretion of the dermal glands forms a

gelatinous envelope, by means of which the animals are able to survive

desiccation. In certain Copepoda and Ostracoda glands of the same type

produce a phosphorescent substance, and others, in certain Amphipoda

and Branchiura, are believed to have a poisonous function. Possibly

related to the same group of structures are the greatly-developed

cement-glands of the Cirripedia, which serve to attach the animals to

their support.

_Phosphorescent Organs._--Many Crustacea belonging to very different

groups (Ostracoda, Copepoda, Schizopoda, Decapoda) possess the power

of emitting light. In the Ostracoda and Copepoda the phosphorescence,

as already mentioned, is due to glands which produce a luminous

secretion, and this is the case also in certain members of the

Schizopoda and Decapoda. In other cases in the last two groups,

however, the light-producing organs found on the body and limbs have a

complex and remarkable structure, and were formerly described as

accessory eyes. Each consists of a globular capsule pierced at one or

two points for the entrance of nerves which end in a central

cup-shaped "striated body." This body appears to be the source of

light, and has behind it a reflector formed of concentric lamellae,

while, in front, in some cases, there is a refracting lens. The whole

organ can be rotated by special muscles. Organs of this type are best

known in the _Euphausiidae_ among the Schizopoda, but a modified form

is found in some of the lower Decapods.

_Reproductive System._--In the great majority of Crustacea the sexes

are separate. Apart from certain doubtful and possibly abnormal

instances among Phyllopoda and Amphipoda, the only exceptions are the

sessile Cirripedia and some parasitic Isopoda (_Cymothoidae_), where

hermaphroditism is the rule. Parthenogenesis is prevalent in the

Branchiopoda and Ostracoda, often in more or less definite seasonal

alternation with sexual reproduction. Where the sexes are distinct, a

more or less marked dimorphism often exists. The male is very often

provided with clasping organs for seizing the female. These may be

formed by the modification of almost any of the appendages, often the

antennules or antennae or some of the thoracic limbs, or even the

mandibular palps (some Ostracoda). In addition, some of the appendages

in the neighbourhood of the genital apertures may be modified for the

purpose of transferring the genital products to the female, as, for

instance, the first and second abdominal limbs in the Decapoda. In the

higher Decapoda the male is generally larger than the female and has

stronger chelae. On the other hand, in other groups the male is often

smaller than the female. In the parasitic Copepoda and Isopoda the

disparity in size is carried to an extreme degree, and the minute male

is attached, like a parasite, to the enormously larger female.

The Cirripedia present some examples of sexual relationships which are

only paralleled, in the animal kingdom, among the parasitic

Myzostomida. While the great majority are simple hermaphrodites,

capable of cross and self fertilization, it was discovered by Darwin

that, in certain species, minute degraded males exist, attached within

the mantle-cavity of the ordinary individuals. Since these dwarf males

pair, not with females, but with hermaphrodites, Darwin termed them

"complemental" males. In other species the large individuals have

become purely female by atrophy of the male organs, and are entirely

dependent on the dwarf males for fertilization. In spite of the

opinion of some distinguished zoologists to the contrary, it seems

most probable that the separation of the sexes is in this case a

secondary condition, derived from hermaphroditism through the

intermediate stage represented by the species having complemental

males.

The gonads, as in other Arthropoda, are hollow saccular organs, the

cavity communicating with the efferent ducts. They are primitively

paired, but often coalesce with each other more or less completely.

The ducts are present only as a single pair, except in one genus of

parasitic Isopoda (_Hemioniscus_), where two pairs of oviducts are

found. Various accessory structures may be connected with the efferent

ducts in both sexes. The oviducts may have diverticula serving as

receptacles for the spermatozoa (in cases where internal impregnation

takes place), and may be provided with glands secreting envelopes or

shells around the eggs. The male ducts often have glandular walls,

secreting capsules or spermatophores within which the spermatozoa are

packed for transference to the female. The terminal part of the male

ducts may be protrusible and act as an intromittent organ, or this

function may be discharged by some of the appendages, as, for

instance, in the Brachyura.

[Illustration: FIG. 11.--Side view of Crab, the abdomen extended and

carrying a mass of eggs beneath it; e, eggs. (After Morse.)]

The position of the genital apertures varies very greatly in the

different groups of the class. They are farthest forward in the case

of the female organs of the Cirripedia, where the openings are on the

first thoracic (fourth postoral) somite. The most posterior position

is occupied by the genital apertures of certain Phyllopoda

(_Polyartemia_), which lie behind the nineteenth trunk-somite. It is

characteristic of the Malacostraca that the position of the genital

apertures is constantly different in the two sexes, the female

openings being on the sixth, and those of the male on the eighth

thoracic somite.

Very few Crustacea are viviparous in the sense that the eggs are

retained within the body until hatching takes place (some Phyllopoda),

but, on the other hand, the great majority carry the eggs in some way

or other after their extrusion. In some Phyllopoda (_Apus_) egg-sacs

are formed by modification of certain of the thoracic feet. The eggs

are retained between the valves of the shell in some Phyllopoda and in

the Cladocera and Ostracoda, and they lie in the mantle cavity in the

Cirripedia. In the Copepoda they are agglutinated together into masses

attached to the body of the female. Among the Malacostraca some

Schizopoda, the Cumacea, Tanaidacea, Isopoda and Amphipoda (sometimes

grouped all together as Peracarida) have a marsupium or brood-pouch

formed by overlapping plates attached to the bases of some of the

thoracic legs. In most of the Decapoda the eggs are carried by the

female, attached to the abdominal appendages (fig. 11). A few cases

are known in which the developing embryos are nourished by a special

secretion while in the brood-chamber of the mother (Cladocera,

terrestrial Isopoda).

_Embryology._

The majority of the Crustacea are hatched from the egg in a form

differing more or less from that of the adult, and pass through a

series of free-swimming larval stages. There are many cases, however,

in which the metamorphosis is suppressed, and the newly-hatched young

resemble the parent in general structure. The relative size of the

eggs and the amount of nutritive yolk which they contain are generally

much greater in those forms which have a direct development.

The details of the early embryonic stages vary considerably within the

limits of the class. They are of interest, however, rather from the

point of view of general embryology than from that of the special

student of the Crustacea, and cannot be fully dealt with here.

Segmentation is usually of the superficial or centrolecithal type. The

hypoblast is formed either by a definite invagination or by the

immigration of isolated cells, known as vitellophags, which wander

through the yolk and later become associated into a definite

mesenteron, or by some combination of these two methods. The

blastopore generally occupies a position corresponding to the

posterior end of the body. The mesoblast of the cephalic (naupliar)

region probably arises in connexion with the lips of the blastopore

and consists of loosely-connected cells or mesenchyme. In the region

of the trunk, in many cases, paired mesoblastic bands are formed,

growing in length by the division of teloblastic cells at the

posterior end, and becoming segmented into somites. The existence of

true coelom-sacs is somewhat doubtful. The rudiments of the first

three pairs of appendages commonly appear simultaneously, and, even in

forms with embryonic development, they show differences in their mode

of appearance from the succeeding somites. Further, a definite

cuticular membrane is frequently formed and shed at this stage, which

corresponds to the nauplius-stage of larval development.

[Illustration: FIG. 12.--Nauplius of a Prawn (_Penaeus_). (Fritz

Muller).]

The larval metamorphoses of the Crustacea have attracted much

attention, and have been the subject of much discussion in view of

their bearing on the phylogenetic history of the group. In those

Crustacea in which the series of larval stages is most complete, the

starting-point is the form already mentioned under the name of

_nauplius_. The typical nauplius (fig. 12) has an oval unsegmented

body and three pairs of limbs corresponding to the antennules,

antennae and mandibles of the adult. The antennules are uniramous, the

others biramous, and all three pairs are used in swimming. The

antennae have a spiniform or hooked masticatory process at the base,

and share with the mandibles, which have a similar process, the

function of seizing and masticating the food. The mouth is overhung by

a large labrum or upper lip, and the integument of the dorsal surface

of the body forms a more or less definite dorsal shield. The paired

eyes are, as yet, wanting, but the unpaired eye is large and

conspicuous. A pair of frontal papillae or filaments, probably

sensory, are commonly present.

A nauplius larva differing only in details from the typical form just

described is found in the majority of the Phyllopoda, Copepoda and

Cirripedia, and in a more modified form, in some Ostracoda. Among the

Malacostraca the nauplius is less commonly found, but it occurs in the

_Euphausiidae_ among the Schizopoda and in a few of the more primitive

Decapoda (_Penaeidea_) (fig. 12). In most of the Crustacea which hatch

at a later stage there is, as already mentioned, more or less clear

evidence of an embryonic nauplius stage. It seems certain, therefore,

that the possession of a nauplius larva must be regarded as a very

primitive character of the Crustacean stock.

As development proceeds, the body of the nauplius elongates, and

indications of segmentation begin to appear in its posterior part. At

successive moults the somites increase in number, new somites being

added behind those already differentiated, from a formative zone in

front of the telsonic region. Very commonly the posterior end of the

body becomes forked, two processes growing out at the sides of the

anus and often persisting in the adult as the "caudal furca." The

appendages posterior to the mandibles appear as buds on the ventral

surface of the somites, and in the most primitive cases they become

differentiated, like the somites which bear them, in regular order

from before backwards. The limb-buds early become bilobed and grow out

into typical biramous appendages which gradually assume the characters

found in the adult. With the elongation of the body, the dorsal shield

begins to project posteriorly as a shell-fold, which may increase in

size to envelop more or less of the body or may disappear altogether.

The rudiments of the paired eyes appear under the integument at the

sides of the head, but only become pedunculated at a comparatively

late stage.

The course of development here outlined, in which the nauplius

gradually passes into the adult form by the successive addition of

somites and appendages in regular order, agrees so well with the

process observed in the development of the typical Annelida that we

must regard it as being the most primitive method. It is most closely

followed by the Phyllopods such as _Apus_ or _Branchipus_, and by some

Copepoda.

[Illustration: FIG. 13.--Early Stages of _Balanus_. (After Spence

Bate.)

A, Nauplius. e, Eye.

B, _Cypris_-larva with a bivalve shell and just before becoming

attached (represented feet upwards for comparison with E, where it

is attached).

C, After becoming attached, side views.

D, Later stage, viewed from above.

E, Side view, later stage and with cirri extended.