CHAPTER XIV

GENERAL CONSIDERATIONS AND CONCLUSIONS

In the preceding chapters certain matters had to be taken for granted,

since it was not possible, or desirable, at the time to discuss more

fully some of the terms that are in common use, or to analyze more

completely many of the phenomena. It was also not necessary to give the

general point of view under which the phenomena were considered in their

physical, chemical, or even causal connection. Little harm has, I trust,

been done by relegating such questions to the final chapter. An attempt

will now be made to give more explicit statements in regard to the use

and meaning of such terms as “organization,” “polarity,” “factors,”

“formative forces,” “vitalistic” and “mechanical principles,”

“adaptation,” etc.

It will be found that the hypotheses that have been advanced to account

for the phenomena of development and of regeneration may be roughly

classified under two heads: first, those in which the organization is

“explained” as the result of the collective action of smaller units; and

second, those in which the organization is itself regarded as a single

unit that controls the parts. Let us examine these points of view more

in detail, in order to see what has been meant in each case by “the

organization.”

A favorite method of biological speculation in the last forty years has

been to refer the properties of the organism to invisible units, and to

explain the action of the organism as the resultant of their behavior.

The hypothesis of atoms and of molecules, by means of which the chemist

accounts for his reactions, has proved so exceedingly fruitful as a

working hypothesis that it has had, I think, a profound influence on the

mind of many biologists, who have, consciously or unconsciously,

attempted to apply a similar conception to the structure of living

organisms. The discovery that all of the higher organisms are made up of

smaller units, the cells, and that the lower organisms are single,

isolated cells, comparable to those that make up the higher forms, has

also drawn attention to the idea that the whole organism is the result

of the action of its units. Furthermore, within the cells themselves

units of a lower order have also been discovered, such, for instance, as

the chromosomes, the chlorophyl bodies, etc., that repeat on a smaller

scale some of the fundamental properties of the entire organism, as

growth and division. It has been assumed that still farther down in the

structure there are smaller units having the same properties, and the

smallest of these are the ultimate units. The organism is looked upon as

the result of the properties of these minute germs. The gemmules of

Darwin furnish an example of an hypothesis of this sort; also the

intracellular pangens of De Vries, the plasomes of Wiesner, the biophors

of Weismann, the idiosomes of Hertwig, and the micellæ of Nägeli are

other examples of this way of interpreting the organization. These

elements are endowed by their inventors with certain properties, and

these are of such a sort that they give the appearance of an explanation

to organic phenomena. It is useless to object to these hypotheses that

they are purely ideal, or fictitious, and that those properties have

been assigned to the germs that will bring about the desired

explanation, and have not been shown to be the real properties of the

germs themselves. But apart from the arbitrariness of the process, it

cannot be claimed that a single one of these creations has been shown to

be true, or has even been accepted by zoologists as probable. A more

serious objection to this point of view is that the most fundamental

characteristics of the organism, those that concern growth, development,

regeneration, etc., seem to involve in many cases the organism as a

whole. So many examples of this have been given in the preceding pages,

that it is not necessary to go over the ground again. It has been shown

that a change in one part takes place in relation to all other parts,

and it is this interconnection of the parts that is one of the chief

peculiarities of the organism. In phenomena of this kind even the cells

seem to play a secondary part, and if so, we can, I think, safely leave

out of account the smaller units of which the protoplasm is supposed to

be built up and we can neglect them, if for no other reason than this,

that the argument that has called them into existence starts out with

the cell as the highest unit. If the cell can be thrown out, most

probably the units of which the cell itself is supposed to be made up

can be safely disregarded also.

It may be objected that only through a knowledge of the minute structure

of the organism can we hope to understand the behavior of the whole; but

my point of view is not that there may not be a fundamental structure,

but that this is not formed by a repetition of elements, which give to

the whole its fundamental properties. It can be shown, I think, with

some probability that the forming organism is of such a kind that we can

better understand its action when we consider it as a whole and not

simply as the sum of a vast number of smaller elements. To draw again a

rough parallel; just as the properties of sugar are peculiar to the

molecule and cannot be accounted for as the sum total of the properties

of the atoms of carbon, hydrogen, and oxygen of which the molecule is

made up, so the properties of the organism are connected with its whole

organization and are not simply those of its individual cells, or lower

units.

The strongest evidence in favor of this view is found in the behavior of

small pieces of an egg, or of a protozoon, or even of a many-celled

organism. A lower limit of organization is very soon reached, below

which the piece fails to produce the characteristic form, although all

the necessary elements are present in the piece to produce the entire

structure. The size of these pieces is enormously large as compared with

the size of the cell, or of the imaginary elements of Nägeli, Weismann,

Wiesner, etc. These results indicate that the organization is a

comparatively large structure.

A few writers have either ignored the presence of smaller units, or have

dealt with the organism from a purely chemical and physical point of

view. They attempt to account for the changes in the organism as the

outcome of known physical and chemical principles. It must, of course,

be granted that in a sense the properties of the organism are the result

of the material basis of the organism; but in another sense this idea

gives a false conception of the phenomena of life, because, if we were

simply to bring together those substances that we suppose to be present

in the organism we have no reason to think that they would form an

organism, or show the characteristic reactions of living things. Even

from a chemical point of view we can see how this result could not be

expected, for it is well known that the order in which a compound is

built up, _i.e._ the way in which the atoms or molecules are introduced

into the structure, is an important factor in the making of the

compound. When we remember the immense period of time during which the

organisms living at present have been forming, we can appreciate how

futile it will be to attempt to explain the behavior of the organism

from the little we know in regard to its chemical composition. Its chief

properties are the result of its peculiar structure, or the way in which

its elements are grouped. This structure has resulted from the vast

number of influences to which the organism has been subjected, and while

it may be granted that if we could artificially reproduce these

conditions an organism having all the properties that we associate with

living things would result, yet the problem appears to be so vastly

complicated that few workers would have the courage to attempt to

accomplish the feat of making artificially such a structure. To prevent

misunderstanding, it may be added that while from the point of view here

taken, we cannot hope to explain the behavior of the organism as the

resultant of the substances that we obtain from it by chemical analysis

(because the organism is not simply a mixture of these substances), yet

we have no reason to suppose that the organism is anything more than the

expression of its physical and chemical structure. The vital phenomena

are different from the non-vital phenomena only in so far as the

structure of the organism is different from the structure of any other

group of substances.

Nägeli has stated that each part acts as though it _knew_ what the other

parts are doing. His idea of the idioplasm involves a conception of the

organism as a whole and not simply the sum total of a number of parts.

Hertwig, who maintained at one time that the development of the embryo

is the resultant of the action of the cells on each other, admits in his

work on _Die Zelle und die Gewebe_ that while this is in part true, yet

on the other hand the whole also exerts an influence on its parts.

Driesch, who hypothetically suggested at one time that the nuclei act as

centres of control of the cell by means of enzymes, has later adopted a

widely different view. Whitman has made a strong argument to the effect

that the cell theory is too narrow a standpoint from which to treat the

organism, and on several occasions I have urged that the organism is not

the sum total of the action and interaction of its cells, but has a

structure of its own independent of that of the cells.

This discussion will suffice to show some of the opinions that have been

held as to the nature of the organization of the organism. Let us next

ask what properties we may ascribe to it.

It has been found that certain polar, or rather dimensional, relations

are characteristic of the organization. The term “polarity” expresses

this in a limited way, but refers only to one line having two

directions, while we now know that the dimensional properties relate to

the three dimensions of space, and for this idea we might make use of

the term heterotropy. Thus we find that a piece of a bilateral animal

regenerates a new anterior end from the part that lay nearer the

anterior end of the original animal, a new right side from the part that

was nearest the original right side, and a new dorsal part from the

region that lay near the original dorsal part, etc.

The polarity of a part can be changed in certain forms, as in tubularia,

by exposing the posterior cut-end to the external factors that bring

about the formation of a hydranth, or, as in hydra, by grafting in a

reversed direction a smaller piece on a larger one. In _Planaria

lugubris_ and in the earthworm the polarity of the new tissue may be

reversed, as compared with that of the part from which it develops, if

the new part arises from certain regions of the body. A curious instance

of the effect of the polarity is shown by the regeneration from an

oblique surface in planarians. The new head arises from the more

anterior part of the new material, rather than from the middle of the

anterior oblique surface, and the new tail arises from the more

posterior part of the posterior oblique surface. As an analysis of this

result has been already attempted in an earlier chapter, it will not be

necessary to go further into this question here.

The development of a new part at right angles to an oblique surface has

also been described, and it has been pointed out that the result appears

to be due to the symmetrical development of the new structure in the new

part. This symmetry of the newly forming part must be also counted as

one of the properties of the organization.

Finally, the mode of regeneration of a new, bifurcated tail in the

teleost, stenopus, shows that the new part may very early become moulded

into the characteristic form, and that the growth of the different parts

is regulated by the structure assumed at an early stage. The new part

does not grow out at an equal rate until it reaches the level of the

notch of the old tail, and then continue to grow at two points to

produce the bilobed form of the tail; but the bilobed condition appears

at the very beginning of the development.

These illustrations give us nearly all the data that we possess at

present on which to build up a conception of the organization. That we

must fail in large part fully to grasp its meaning from these meagre

facts is self-evident. The main difficulty seems to lie in this,--that

when we attempt to think out what the organization is we almost

unavoidably think of it as a structure having the properties of a

machine, and working in the way in which we are accustomed to think of

machines as working. The most careful analysis of the “machine theory,”

as applied to the phenomena of development and of regeneration, has been

made by Driesch. It has been pointed out that in his _Analytische

Theorie_ Driesch assumed that development is due to “given” properties

in the egg; that each stage is initiated by some substance contained in

the egg acting on the stage that has just been completed. That is, each

stage is the condition of the following. The “rhythm” of development is

accounted for in this way. The changes are described as due to chemical

processes (including also ferment actions). The nucleus is supposed to

contain all the different kinds of ferments that act, when set free, as

stimuli on the protoplasm; but since the ferments are always set free at

the propitious moment, Driesch was obliged to assume that the cytoplasm

acts on the nucleus in such a way as to make it produce the proper

ferment for the next stage. Thus the cytoplasm first influences the

nucleus, the latter sets free a specific ferment that starts a new

chemical change in the cytoplasm, and the changed cytoplasm may then

react again on the nucleus, and a different ferment be set free, etc.

Each change is therefore not only an effect of what has gone before, but

the cause of the next process.[132] Driesch points out that it is

necessary at this stage to make a further assumption, because the

cytoplasm must not only be acted upon by the ferment, but it must itself

be of such a sort that it _responds_ to the action. This leads to a

great complication of the phenomena; but the assumption does not depart,

in the last analysis, from the idea of the cell as a system in a

mechanical sense. This assumption of a receiving and an answering

station for the stimuli carries with it the further assumption of a

many-sided “_harmony_.” Without a harmony at each step in the

development there could be no orderly ontogeny. The assumption of this

harmony introduces a new element into the series of hypotheses. The

_appearance_ of a causal explanation was given in those parts of the

argument preceding the introduction of the assumption of a harmony, but

with the admission of this new element into the argument, the causal

point of view is left. Driesch says in this connection: “If we cannot

gain a singleness of view in the way that has been followed, we can

reach this in another way. Indeed, the way of doing so has been already

implied in that part of the theory dealing with the harmony of the

phenomena. The existence of this harmony is inferred, because, in the

large majority of cases, the ontogeny leads to a typical result.

Therefore we must assume that the conditions for the end result are

given--the conditions are the harmony itself.” Put somewhat less

obscurely, if more crudely, we may express Driesch’s idea by saying that

the harmony that stands for a hen is given in the hen’s egg.

Driesch adds: “Because a typical result always follows, therefore every

single step in the ontogeny must be judged, from an analytical

standpoint, from the point of view of the result itself. The result is

the _purpose_ of the ontogeny. It is as though we visited daily a wharf

where a ship is being built,--everything appears a chaos of single

pieces, and we can only understand what we see when we consider what is

to be made. Only from a teleological point of view can we speak of a

development, for this term expresses the very existence of an object to

be developed. The term is used fraudulently if it is intended to mean

that the development is the outcome of ‘processes,’ using this term in

the sense that a mountain or a delta develops from physical processes.”

“We can only reach a satisfactory view of the phenomena when we

introduce the word ‘purpose.’ This means that we must look upon the

ontogeny as a process carried out in its order and quality as though

guided by an intelligence. We arrive at this conclusion, because the

individual whole is ‘given,’ as the clearly recognized goal of the

entire process of development.”

In a later attempt to analyze the problem of development, Driesch

examined it more fully from the point of view of the machine theory.

This contribution must be looked upon rather as a _tour de force_ that

is intended to show how far this idea can be carried in its application

to development. Driesch explains that in his analytical theory he

assumed from what is “given” in the egg that the egg can be understood

causally, as a machine is understood, but what is “given” can be

understood only teleologically. He says: “What I defended was not

vitalism, but, so far as the phenomena of life are concerned, exactly

the current physico-chemical dogmatism; but I did not fail to see and to

point out the consequences of this dogmatism, which every one (except

Lotze) has avoided, viz., that the adaptive basis in which the living

phenomena take place is ‘given.’” Driesch defines his view as

formal-teleological, in contrast to vitalistic. The former may also be

called a machine theory of life in which the _purpose is given, not

explained_.

In later writings Driesch has thrown over some of his earlier

conclusions and adopted a causal-vitalistic philosophy. The basis of

this new conception is found in the proportional development of parts of

an original whole, as has been explained in a preceding chapter. This

result belongs to a category of phenomena that is in principle not

machine-like, but of a specifically different kind. It is something that

cannot be explained by the agencies of the outer world, such as light,

gravity, salinity, temperature, etc. After examining other hypotheses,

Driesch returns to a view that he had previously rejected, viz. the

conception of “position,” by which is meant the influence of the

location in the whole. This position has certain directions, but nothing

in addition that is typical. By the term “location in the whole” is

meant that the word “location” (_Lage_) shall refer not to geometric

space, but to the organization of the object that has its own

directions. A deformation of the whole may change very little the

relative location of the parts.

In his earlier writings Driesch rejected this idea, because it did not

seem to satisfy our etiological need, and also because he thought that

he could reach his goal from the standpoint of initiating stimuli

(_Auslösungen_). Driesch now assumes that the stem of tubularia and the

archenteron of the starfish, for example, have a polar structure.

Bilateral forms, as the whole larva of the starfish, have a coördinated

system of two axes with unlike poles and one axis with like poles, each

of a given length or proportion. The ends of the axes are characteristic

points of the system. If, in such a system, a typical act of

differentiation appears, to which we can assign a cause, so far as the

location is concerned, a change will occur as follows: To take the

simplest case, that of a system with only one axis having unlike poles,

as the archenteron of the starfish, in which differentiation has not

begun, we can picture to ourselves the formation of the divisions of the

archenteron in a causal way by supposing the end of the axis, or pole,

to be the location (_Sitz_) of an initiative “action at a distance”

(_auslösende Fernkraft_). This locality, just because it is the end of a

system, is something special; and it acts in such a way that wherever an

effect is produced, it is the cause of that effect. This very way of

looking at the problem postulates a sort of causal harmony. But how, it

may be asked, can a special point or pole of an axis bring about an

action in the system? This can be shown by means of a simple case, viz.

the dividing up of the archenteron of the starfish into its

characteristic parts. There are two effects produced, viz. the formation

of the two constrictions of the wall. We need not consider the fact that

the constrictions are formed, for this is established in the potence of

the system, and is awakened by the initiating cause, but the place at

which the constrictions are produced is that for which we should

account. We must think of this cause as “action at a distance,” and

indeed as an “action at a distance” that works at a determinate, typical

distance. This inherent measure of distance of the action is not one of

absolutely fixed size, for a gastrula made shorter by an operation also

subdivides into proportionate parts. The action starts from the poles of

the system, and acts, not at an absolute, but at a relative distance,

since it is dependent upon the length of the axis of the whole

differentiating system. “The localization of ontogenetic processes is a

problem _sui generis_. The phenomenon can always be expressed on the

scheme of cause and effect, if we assume the ‘action at a distance’ to

start from fixed points of a differentiating system.”

In regard to the criterion of vitalistic phenomena Driesch makes the

following statement: “On the current view we are inclined to see, in the

formative changes, actual causes at work that even initiate those

processes that we call stimuli; we do so because we pretend at present

to know something of the special mechanism by which the formative

changes work. The effects come into play through a causal union of

simple processes of a physical-chemical sort that we may call a chain of

stimuli. From the new point of view, the initiatory stimulus is not an

initiatory cause or the effect of a causally united chemico-physical

phenomenon. The stimulus is, from this point of view, a true stimulus,

but the effect is not a true effect of its initiation, but is rather to

be designated a responsive effect, for there is no connecting chain of

stimuli. It is in the place of the latter that the vitalistic view

appears. The only data of a machine sort in the conception are the

arrangements for the reception and guidance of the stimulus, perhaps

also the means for carrying out the response effect; for the machine

data are only the prerequisites of the phenomena, but in themselves do

not bring about the result.”

Driesch finds in this argument a _demonstration_ of the vitalistic

doctrine, but vitalism, of course, of a very special kind. Without a

more elaborate presentation of his view it is not possible to give a

detailed criticism of his conclusions; but a few of the more obvious

objections that may be brought against this view may be discussed. The

assumption of “action at a distance” does not, I think, in any way help

to make the phenomenon clearer. The formation of a typical larva of

normal proportions from a piece of an egg is just as mysterious after

the assumption of an “action at a distance” of a proportionate sort as

it was before. Driesch has introduced into the argument to establish a

vitalistic standpoint one of the most obscure ideas of physical science.

There is, so far as I can see, no necessity for such an assumption,

since there is present in every case a continuous medium of protoplasm,

which would seem to make this idea at least superfluous. Moreover, the

additional element that Driesch has added to his conception of the

process, namely, an action in proportion to the size of the piece, is

objectionable if for no other reason than that it attributes to the

unknown principle of “action at a distance” a quality that is the very

thing that ought itself to be explained. This assumption, it seems to

me, begs the entire question, and we can give no better explanation why

it should belong to the principle of “action at a distance” than to

anything else. Far from having given a demonstration of vitalism,

Driesch has, I think, in his analysis simply set up an entirely

imaginary principle, which, taken in connection with other

undemonstrable qualities, is called vitalism.

If we cannot accept Driesch’s demonstration of vitalism, from what point

of view can we deal with the phenomenon of the production of a typical

form from each kind of living material? Can we find a physico-chemical

explanation of the phenomenon? Enough has been said to show that this

property is one of the fundamental characteristics of living things and

is, in all probability, a phenomenon which we certainly cannot at

present hope to explain. Yet the question raised by Driesch is, at

bottom, not so much whether we can give a physico-chemical explanation,

but whether the phenomenon belongs to an entirely different class of

phenomena from that considered by the physicist and by the chemist. Let

us examine the results and see if we are really forced to conclude that

there is no other physico-causal point of view possible.

In many cases in which a response to an external stimulus takes place,

we must assume a physico-causal connection between the stimulus and the

effect. The action of poisons, for instance, is an example of this

kind, and, in some cases, as in the formation of the galls of plants,

the stimulus of a foreign body may lead to the development of a

structure, the gall, of a definite form. The experiments of Herbst on

the effect of lithium salts in sea water on the development of the

sea-urchin embryo lead to a similar conclusion. The changes in form that

result from other external agents, such as light, gravity, contact,

etc., can be best understood from a physico-causal point of view, and it

seems improbable at least that their action within the organ is

transformed into a vitalistic causal action through Driesch’s principle

of an “action at a distance.”[133] The effect of internal factors on the

change of form is, however, much more difficult to deal with, since we

know so little at present about these factors. Here we find amongst

other phenomena that of the proportionate formation of a whole organ

from a part of an old one, or of an egg. We find it difficult, if not

impossible, to attribute this directly to external causes, yet, as I

have tried to show, the first steps through which this takes place can

be referred to physico-causal principles. These are the separation of

the piece from the whole; the change of the unsymmetrical piece into a

symmetrical one, brought about, in part at least, by contractile

phenomena in the piece, aided, no doubt, in some cases by surface

tension, etc. These changes give the basis for the development of a new

organization along the lines of structure that are already present in

the piece. We find here the beginning of a physico-causal change, and,

so far as I can see, we have no reason to suppose that at one stage in

the process this passes over into the vitalistic-causal principle. It

should, I think, be pointed out in this connection that even in the

physical sciences it would not be difficult to establish a vitalistic

principle, or whatever else it might be called, if we chose to take into

account such properties of bodies as those which the chemist calls the

affinities of atoms and molecules, or the symmetrical deposition of

material on the surface of a crystal from a supersaturated solution,

etc. These phenomena are usually looked upon as “given,” that is, beyond

the hope of possible examination. Until these questions are more fully

understood scientists are, I think, justified in showing a certain

amount of self-restraint in regard to the solution of such problems. Du

Bois-Reymond has summed up this point of view in the dictum,

“Ignorabimus,” which is interpreted to mean, not only that we are

ignorant at present on certain questions, but that we know we must

remain ignorant. The formative changes in the organism appear to belong

to this category of questions. This confession of ignorance need not

mean that we cannot hope to discover the conditions under which the

phenomena take place, so that we can predict with certainty what the

results will be, but the meaning of the change itself may remain

forever obscure, at least from our present conception of

physico-chemical principles. Shall we, therefore, call ourselves

vitalists, because we find certain phenomena that we cannot hope to

explain as the result of physical principles, or for which we must

invent an unknown principle? Or can we succeed in demonstrating a

different kind of principle in living things? If we could, we might be

justified in calling ourselves by the name of vitalists. But who has

made such a discovery? Does the well-known phenomenon of proportionate

development give a demonstration of the unknown principle? Would one be

justified in claiming a different principle that is not a physico-causal

one, because the nerve impulse is different from any known physical

phenomenon? The preceding pages have made clear, I hope, that, for my

own part, I see no grounds for accepting a vitalistic principle that is

not a physico-causal one, but perhaps a different one from any known at

present to the physicist or chemist.

* * * * *

In order to make clear in what way certain terms have been used in the

preceding chapters, it may not be out of place to indicate how it is

intended that they should be employed. The word “cause” has been used in

the sense in which the physicist uses the term. A “stimulus” is the

chain of effects of a cause acting on a living body. In certain cases

the cause itself may be spoken of as the stimulus, but only when its

specific action on a living body is implied. A “factor” is a more

general term and is usually one or more of a number of causes that

produce a result. It may prove convenient to use this term where a

change in form is produced. Thus the size of a piece is one of the

factors that determines the result; the part of the body from which the

piece is taken may also be a factor, or rather the kind of material

contained in the piece. These examples will suffice to show that the

word is used for an observed connection of a very general sort,

especially for those cases in which we have not analyzed the factor into

its components. The term is especially useful for cases in which the

change in form is the outcome of the innate properties of the

organization. The term may be used so that it need not prejudice the

result, either in favor of a physico-causal or a vitalistic-causal point

of view. It may be convenient to use it as an indifferent term in these

respects. The word “force” I have attempted to avoid as far as possible,

except in such current expressions as “the force of gravity,” etc., for,

apart from the loose way in which the word is used even by physicists,

we know so little about the forces in the organism that it is best, I

think, to use the word as sparingly as possible, and only where a known

physical force can be shown to produce an effect.

Much misunderstanding has arisen in connection with the term “formative

force.” In the first place we naturally associate with this term the

meanings attached to it by writers of the seventeenth and eighteenth

centuries. They assumed a formative principle in living things, that is

an expression of a formative force. Roux, who has more recently used the

term, has attempted to avoid misunderstanding by using the plural,--“the

formative forces of the organism”; but even under these circumstances,

differences of opinion have arisen, as shown by the controversy between

Roux (’97) and Hertwig (’94 and ’97), on this point. A change in form

carries with it a change of position of the parts, and the latter

involves the idea of forces, but the nature of these forces is entirely

obscure to us, at least we cannot refer them to any better-known

category of physical or chemical forces. They may, perhaps, be most

profitably compared to the forces of chemical union, but whether they

are very numerous or can be reduced to a limited number of kinds of

force, we do not know. If it could be shown that the changes in the

organism are due to molecular changes, then the formative forces might

appear to be only molecular forces, but we are not in position at

present to demonstrate that this is the case, however probable it may

appear.

Finally, the use of the term “organization” may be considered, although

from what has been said already it is clear that there must be a certain

amount of vagueness connected with our idea of what the organization can

be. The organization, from the point of view that I have adopted, is a

structure, or arrangement of the material basis of the organism, and to

it are to be referred all the fundamental changes in form, and perhaps

of function as well. We also use the term as applied to the completed

structure, by which we mean that the organism consists of typical parts

having a characteristic arrangement carrying out definite functions.

When applied to the egg, or to a regenerating piece, the term refers to

some more subtle structure that we are led to suppose to be present from

the mode of behavior of the substance. As pointed out, we know this

organization at present from only a few attributes that we ascribe to

it, and are not in a position even to picture to ourselves the

arrangement that we suppose to exist.

_REGENERATION AND ADAPTATION_

One of the most difficult questions with which the biologist has to deal

is the meaning of the adaptation of organisms to their environment.

Pflüger, in an article entitled “The Teleological Mechanics of Living

Nature,” has drawn attention to the teleological character, or

purposefulness, of certain processes in the living organism. “There has

been found only one general point of view, which if not absolute, yet is

the rule, to account for the eternal transformations of energy in the

living body. Only those combinations of causes take place that are as

favorable as possible for the welfare of the animal. This holds true

even when entirely new conditions are artificially introduced into the

living organism. What is more remarkable than that, even in the highly

organized mammal, there should be a regeneration of the bile duct after

its removal, or that after a large piece of a nerve has been extirpated

by a severe operation it should be again renewed?... What is more

surprising than that the organism should become accustomed to the most

diverse kinds of organic and inorganic poisons?... And, finally, there

are a number of facts that make good the law that changes appear to be

governed by no other principle than the purpose of making certain the

existence of the organism.”

Pflüger’s teleological law of causality is that “the cause of every need

of a living being is at the same time the cause of the fulfilment of the

need.” Pflüger explains that the word “cause” is here intentionally

chosen in order to bring out the necessary, lawful connection in which

the cause of each need stands in relation to the fulfilment of that

need. He adds that it would have been more correct, but less pointed, to

have said “motive” or “inducement” instead of “cause.”

In order to illustrate what is meant by this law, the following examples

may be given. Food and water bring back the organism to its normal

condition. The absence of food in the body leads to hunger, and this to

the taking in of more food; or, in other words, the need of food leads

to the search for food, or at least to the taking in of food. The sexual

desire, or the need to reproduce, brings about the condition of the

animal that leads to reproduction. A defect in the valves of the heart

leads to the enlargement of the right or the left ventricle. The removal

of one kidney leads to the hypertrophy and increased function of the

other. And although not explicitly stated by Pflüger in this place, we

may add to this list the removal of a part of an animal, that leads to

the regeneration of that part. Pflüger further states that we are making

no subtle distinction when we point out that these phenomena, if looked

at from the point of view of purposeful acts, appear to have a

teleological side. In reply to this it may be stated, however, that in

certain cases of regeneration it can be shown that the result is

entirely useless, or even injurious to the organism; hence the

teleological nature of the process is entirely lost sight of, and we are

the more ready to accept a simple causal explanation of the phenomena.

The best example of this that I can give is the development of a tail at

the anterior end of a posterior piece of an earthworm. This process is

not an occasional one, but is constant. An example of an apparently

useful result, so far as the individual’s well-being is concerned, but

entirely useless from the point of view of the continuance of the

species, is found in the development, in the earthworm, of a new head

after the removal of the anterior end, including the reproductive

region. New reproductive organs are not formed, and, although, in virtue

of the regeneration of a new head, the individual is capable of carrying

on its existence, yet the race of earthworms is not thereby benefited.

The production of two tails in lizards, or of two or more lenses in the

eyes of newts, are examples of the regeneration of superfluous

structures.

If, however, it is claimed that in the large majority of cases the

process of regeneration is for the welfare of the individual, and for

the race also, this must be admitted, and it is this fact which has made

a deep impression on the minds of many biologists.

From the causal point of view, we may look upon the formative changes as

the necessary outcome of strictly causal principles, and we may suppose

that they take place without respect to the final result. But the

question before us is rather to explain, if possible, why the changes

that take place are in so many cases useful ones. That they are not

always useful must be admitted, that they sometimes are must be granted,

and it is the latter alternative that has attracted special attention.

Now it is undoubtedly the simplest solution to claim that the scientist

has nothing to do with the adaptiveness of the response, that his whole

problem lies in a study of the causal phenomena involved in each

process, but it is unquestionably true that scientists have not been

satisfied to confine their hypotheses to this side of the question. The

widespread interest in the theory of natural selection is, I think, due

to the fact that it appears to offer an explanation of the formation of

adaptive processes--not that it pretends to explain the origin of the

adaptive structures or processes themselves, but that it seems to

account for the adaptiveness of the fully formed product, _i.e._ the

organism. For it will be seen that if only those forms (variations)

survive that are useful, and survive either because the environment

selects them (and exterminates the others), or because new forms that

arise find a new place in nature where they can remain in existence,

then the adaptiveness of the form to its surroundings would seem to be

accounted for. In this case we can see how the causal processes that

take place in the organism need have no causal connection with the

environment,--except in the sense that the environment has acted as a

selective agent, and appears, therefore, in the light of a teleological

factor. But, as has been said before, the question is not so much that

organisms _are_ adapted, as that organisms _respond adaptively_ to

changes to which they can never have been subjected before. It is for

the latter fact that a solution is to be sought.

In this whole question there is danger of extending our own experience

as agents in the constructing of products useful to ourselves, to the

organic world, in attempting to account for the way in which the useful

characters of organisms have arisen. We see a ship being built, and we

know that when it is finished it will be useful. We explain its building

by its future usefulness,--that is, we explain the process as the result

of human teleology. But have we any right to extend this principle to

the organic world, and infer that processes are there carried out

_because_ they will ultimately be useful to the individual in which they

take place? Unconsciously we have shifted our point of view. The ship

does not build itself, and the final result of the building is of no use

to the ship. On the contrary, the organism does build itself and the

result is useful only to itself. Unless we suppose that some external

agent acting as we do ourselves directs the formative processes in

animals and plants, we are not justified in extending our experience as

directive agents to the construction of the organic world; and if we are

not justified in drawing such a conclusion, since the organism by no

means always responds adaptively, and in many cases very badly and

incompletely, then, it seems to me, we must look for another point of

view.

In connection with his work on the regeneration of the eye of the

salamander, Gustav Wolff (’93) has made some sweeping statements in

regard to the phenomenon of adaptation. “Purposeful adaptation is that

which makes the organism an organism. It is this adaptation that appears

to us as the most characteristic property of all living things. We can

think of no organism without this characteristic.” In another place he

states, “...we recognize that every explanation that presupposes the

living being, every post-vital explanation of organic adaptation,

presupposes in every case that which it attempts to explain; we

recognize that the explanation of adaptation must coincide with the

explanation of life itself.” There is, perhaps, some truth in this

statement, but, on the other hand, Wolff has, I think, shot somewhat

over the mark. As Fischel (1900) has pointed out, the response is

sometimes not adaptive, as when two lenses develop in the same eye in

the salamander; and, we may add, as when an antenna develops in certain

crustacea in place of an eye, or as when a tail develops instead of a

head, or a head in place of a tail. In the light of these facts, it is,

I think, going too far to assert that the power of living things to

respond adaptively to changes in themselves or in their environment is

synonymous with life itself. All that we can fairly claim is that in

several cases living forms have been shown to be able to _complete

themselves_, and this may be _interpreted_ as an adaptive response. It

would carry us far beyond the scope of the present volume to discuss the

question of adaptation in general, and I think it highly probable that

it will prove true that there are many kinds of adaptive responses that

must be considered separately and each on its own merits. Let us,

therefore, confine our concluding remarks entirely to _regenerative

changes_ which, after they have been completed, are for the good of the

organisms. Our preceding discussion has led to the conclusion that the

phenomena of regeneration are not processes that have been built up by

the accumulation of small advances in a useful direction; that they

cannot be accounted for by the survival of those forms in which the

changes take place better than in their fellows, for it is often not a

question of life and death whether or not the process takes place, or

even a question of leaving more descendants. On the contrary, it seems

highly probable that the regenerative process is one of the fundamental

attributes of living things, and that we can find no explanation of it

as the outcome of the selective agency of the environment. The phenomena

of regeneration appear to belong to the general category of

growth-phenomena, and as such are characteristic of organisms. Neither

regeneration nor growth can be explained, so far as I can see, as the

result of the usefulness of these attributes to the bodies with which

they are indissolubly associated. The fact that the process of

regeneration is useful to the organism cannot be made to account for its

existence in the organism.

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=Fiedler, K.=

’91. Entwickelungsmechanische Studien an Echinodermeiern.

Festschr. Nägeli u. Kölliker, Zurich, 1891.

=Fischel, A.=

’97. Experimentelle Untersuchungen am Ctenophorenei, 1-4.

Arch. f. Entw.-mech., VI, 1897-98.

’98. Über die Regeneration der Linse. Anat. Anz., XIV,

1898.

=Flemming, W.=

’80. Über Epithelregeneration und sogen. freie

Kernbildung. Arch. f. mikr. Anat., XVIII, 1880.

=Flexner, S.=

’98. The Regeneration of the Nervous System of Planaria

torva and the Anatomy of the Nervous System of Double-headed Forms.

Jour. Morph., XIV, 1898.

=Forest-Heald, F. de.=

’98. A Study of Regeneration as exhibited by Mosses. Bot.

Gaz., XXVI, 1898.

=Fraisse, P.=

’85. Die Regeneration von Geweben und Organen bei den

Wirbelthieren, besonders bei Amphibien und Reptilien. Kassel und

Berlin, 1885.

=Fredericq, L.=

’83. Sur l’autotomie ou mutilation par voie réflexe comme

moyen de défense chez les animaux. Arch. d. Zool. expérim. (Ser. 1),

1883.

’87. L’autotomie chez les étoiles de mer. Revue

Scientifique (Ser. 3), XIII, 1887.

’93. L’autotomie ou la mutilation dans le règne animal.

Bull. de l’Acad. roy. de Belgique (Ser. 3), XXVI, 1893.

=Frenzel, J.=

’91. Über die Selbstverstümmelung (Autotomie) der Thiere.

Arch. f. d. Ges. Physiol., L, 1891.

=Friedländer, B.=

’95. Über die Regeneration herausgeschnittener Theile des

Central nerven-systems von Regenwürmern. Zeit. f. Wiss. Zool. LX, 1895.

’98. Über den sogennanten Palolowurm. Biol. Cent., XVIII,

1898.

’99. Nochmals der Palolo, etc. Biol. Centralbl., XIX,

1899.

=Fuhrmann, M.=

’98. Sur les phénomènes de la régénération chez les

Invertébrés. Arch. Sc. Nat., V, 1898.

=Gachet, M. H.=

’34. Mémoire sur la reproduction de la queue des reptiles

sauriens. Actes de la société linnéenne de Bordeaux, Nr. 36, 25

Juillet, 1834.

=Gayat, M. J.=

’73. Experimentalstudien über

Linsenregeneration. Klin. Monatsbl. für Augenheilk., 1873.

=Gesner, Conrad.=

1686. Historiae animalium. Lib. II, MDCLXXXVI.

=Giard, A.=

’95. Polydactylie provoquée chez Pleurodèles Walthii

Mich. Compt. Rend. Soc. Biol., II, 1895.

’96. Y a-t-il antagonisme entre la “Greffe” et la

“Régénération.” _Ibid._, 1896.

’97. Sur les régénérations hypotypiques. _Ibid._, IV,

1897.

’97. Sur l’autotomie parasitaire, etc. _Ibid._, 1897.

=Glückselig, M. Ch.=

’63. Über das Leben der Eidechsen, Verhandl. d.

zool.-bot. Vereins in Wien., XIII, 1863.

=Godelmann, R.=

’01. Beiträge zur Kenntniss von Bacillus Rosii Fabr. mit

besonderer Berüchsichtigung der bei ihm vorkommenden Autotomie und

Regeneration einzelner Gliedmassen. Arch. f. Entw.-mech., XII, 1901.

=Goebel, K.=

’98. Organographie der Pflanzen. I. Allgemeine

Organographie, Jena, 1898.

=Goette, A.=

’69. Über Entwickelung und Regeneration des

Gliedmassenskeletts der Molche. Tübingen, 1869.

=Gonin, J.=

’96. Étude sur la Régénération du cristallin. Ziegler’s

Beiträge z. pathol. Anat., XIX, 1896.

=Goodsir, H. D. S.=

’44. A Short Account of the Mode of Reproduction of Lost

Parts in the Crustacea. Ann. and Mag. Nat. Hist., XIII, 1844.

=Graber, V.=

’67. Zur Entwickelungsgeschichte und

Reproductionsfähigkeit der Orthopteren. Berichte d. kaiserl. Akad. d.

wiss. Wien. LV, 1867.

=Greef, R.=

’67. Über Actinosphaerium Eichhornii, etc. Arch. f. Mikr.

Anat., III, 1867.

=Griffini e Marchio.=

’99. Sulla rigenerazione totale della retina nei tritoni.

Riforma med., 1899.

’99. Sur la régénération de la rétine chez les tritons.

Arch. ital. de Biolog., XII.

=Gruber, A.=

’84-’5. Über Künstliche Theilung bei Infusorien, I.

Biolog. Centralbl., IV, 1884-85.

’85-’6. Same, Part II. _Ibid._, V, 1885-86.

’86. Beiträge zur Kenntniss der Physiologie und Biologie

der Protozoen. Ber. Nat. Ges. Freiburg, I, 1886.

’87. Mikroskopische Vivisektion. Ber. d. Naturfor.

Gesell. zu Freiburg, II, 1887.

=Haeckel, E.=

’68. Monographie der Moneren. Jena Zeit. f. Naturwiss.,

IV, 1868.

’69. Entwickelungsgeschichte der Siphonophoren (page 73),

1869.

’78. Die Kometenform der Seesterne und der

Generationswechsel der Echinodermen. Zeit. f. wiss. Zool., XXX, 1878.

=Hargitt, C. W.=

’97. Recent Experiments on Regeneration. Zool. Bull., I,

1897.

’99. Experimental Studies upon Hydromedusae. Biolog.

Bull., I, 1899.

=Harrison, R. G.=

’98. The Growth and Regeneration of the Tail of the Frog

Larva. Arch. f. Entw.-mech., VII, 1898.

=Hasse, H.=

’98. Über Regeneration bei Tubifex rivulorum. Zeit. wiss.

Zool., LXV, 1898.

=Hazen, A. P.=

’99. The Regeneration of a Head

instead of a Tail in an Earthworm. Anat. Anz., XVI, 1899.

=Heider, K.=

’97. Ist die Keimblätterlehre erschüttert? Zool.

Centralb., IV, 1897.

=Heineken, C.=

’28-’29. Experiments and Observations on the Casting off

and Reproduction of the Legs in Crabs and Spiders. The Zool. Journal,

IV, 1828-29.

=Hepke, P.=

’97. Über histo- und organogenetische Vorgänge bei den

Regenerationsprozessen der Naiden. Zeit. wiss. Zool., LXV, 1897.

=Herbst, C.=

’94. Über die Bedeutung der Reizphysiologie für die

kausale Auffassung von Vorgängen in der tierischen Morphologie. Biol.

Centralb., XIV und XV, 1894 u. 1895.

’95-’99. Über die Regeneration antennenähnlicher Organe

an Stelle von Augen. I. Arch. f. Entw.-mech., II, 1895.

’96. II. Versuche an Sicyonia sculpta. Vierteljahrsschr.

d. Naturf.-Ges., Zurich, 1896.

’99. III u. IV. Weitere Versuche, u. s. w. Arch. f.

Entw.-mech., IX, 1899.

’96. Experimentelle Untersuchungen über den Einfluss der

veränderten chemischen Zusammensetzung, etc. Arch. Entw.-mech., II,

1896.

’97. Über die zur Entwickelung der Seeigellarven

nothwendigen anorganischen Stoff, I. _Ibid._, V, 1897.

=Herculais, K. d’.=

’75. Recherches zur l’organisation et la developpement

des volucelles, 1875.

=Herlitzka, A.=

’96. Contributo allo studio della capacita evolutiva dei

due primi blastomeri nell’uovo di tritoni (triton cristatus). Arch. f.

Entw.-mech., II, 1896.

=Herrick, F. H.=

’95. The American Lobster. Bull. U. S. Fish Commission,

1895.

=Hertwig, O.=

’85. Das Problem der Befruchtung und der Isotropie des

Eies. Jena Zeit., XVIII, 1885.

’85. Welchen Einfluss übt die Schwerkraft auf die

Teilungen der Zellen? _Ibid._, 1885.

’90. Experimentelle Studien am tierischen Ei vor, während

und nach der Befruchtung. _Ibid._, XXIV, 1890.

’92. Urmund und Spina bifida. Arch. f. mikr. Anat. XXXIX,

1892.

’92. Ältere und neuere Entwickelungstheorien. Rede.

Berlin, 1892.

’93. Über der Wert der ersten Furchungszellen für die

Organbildung des Embryo. Arch. f. mikr. Anat. XLII, 1893.

’94. Zeit- und Streitfragen der Biologie, I. Präformation

oder Epigenesis? Jena, 1894.

’95. Beiträge zur experimentellen Morphologie und

Entwickelungsgeschichte. I. Die Entwickelung des Froscheies unter dem

Einfluss schwächerer und stärkerer Kochsalzlösungen. Arch. f. mikr.

Anat., XLIV, 1895.

’96. Experimentelle Erzeugung tierischer Missbildung.

Festschr. Gegenbaur., II, 1896.

’97. Zeit- und Streitfragen, II. Mechanik und Biologie,

Jena, 1897.

’98. Über den Einfluss der Temperature auf die

Entwinkelung von Rana fusca und Rana esculenta. Arch. f. mikr. Anat.,

LI, 1898.

’98. Die Zelle und Die Gewebe. II. Allgemeine Anatomic

und Physiologie der Gewebe. Jena, 1898.

’98. Beiträge, etc., IV. Über einige durch

Centrifugalkraft in der Entwickelung des Froscheies hervorgerufene

Veränderungen. Arch. f. mikr. Anat., LIII, 1898.

=Hescheler, K.=

’96-’98. Über Regenerationvorgänge bei Lumbriciden, I u.

II. Jena. Zeit., XXX, 1896, und XXXI, 1898.

=Hirota, S.=

’95. Anatomical Notes on the “Comet” of Linkia Multifora.

Zool. Mag. Tokyo, VII, 1895.

=His, W.=

’75. Unsere Körperform und das

physiologische Problem ihrer Entstehung. Leipsig, 1875.

=Hofer, B.=

’89. Experimentelle Untersuchungen über den Einfluss des

Kerns auf das Protoplasma. Jena. Zeitsch. f. Naturf. (N. F.), XVII,

1889.

=Horst, R.=

’86. Zur Regenerationslitteratur. Zool. Anz., IX, 1886.

=Hoy, P. R.=

’71. The Development of Amblystoma lurida. The American

Naturalist, 1871.

=Hubrecht, A. A. W.=

’87. Report on the Nemertines. Reports of the Challenger

Expedition, 1887.

=Ischikawa, C.=

’90. Trembley’s Umkehrungsversuche an Hydra nach neuen

Versuchen erklärt. Zeit. f. wiss. Zool., XLIX, 1890.

=Joest, E.=

’95. Transplantationsversuche an Regenwürmern. Sitz. ber.

d. Gesell. z. Berf. d. ges. Naturwiss. zu Marburg, 1895.

’97. Transplantationsversuche an Lumbriciden. Arch. f.

Entw.-mech. V, 1897.

=Johnstonus, Joannes.=

1657. Historiae naturalis de quadrupedibus. Amstelodami,

MDCLVII, t. I, lib. IV, c. II, art. I u. art. II.

=Kennel, J. von.=

’82. Über Teilung und Knospung der Tiere. Dorpat, 1882.

’82. Über Ctenodrilus pardalis. Arb. a. d. zool. zoot.

Inst. Würzburg, V, 1882.

’88. Biologische und Faunistische Notizen aus Trinidad.

Arb. d. Zool.-Zoot. Inst., Würzburg, VI, 1888.

=Kinberg, J. G. H.=

’67. Om regeneration af hufvudet och de främre

segmenterna hosen Annulat. Oefversigt af. kongl. Vetenskaps Akadamiens

Förhandlmgar, 1867.

=King, H. D.=

’98. Regeneration in Asterias vulgaris Arch. f.

Entw.-mech., VII, 1898.

’00. Further Studies on Regeneration in Asterias

vulgaris. _Ibid._, IX, 1900.

=Klein, Edm. J.=

’95-’97. Regeneration, Transplantation und Autotomie im

Thierreich. Fauna Luxemburg, 5-7, 1895-97.

=Knight, T. A.=

’09. On the Origin and Formation of Roots. Phil. Trans.,

1809.

=Kny, L.=

’89. Umkehrversuch mit Ampelopsis quinquefolia. Berichte

d. deutsch. botan. Gesellsch., VII, 1889.

=Kochs, W.=

’97. Versuche über Regeneration von Organen bei

Amphibien. Arch. f. mikr. Anat., XLIX, 1897.

=Korschelt, E.=

’97. Über das Regenerationsvermögen der Regenwürmer.

Sitzungsber. Ges. Naturw., Marburg, 1897.

’98. Über Regenerations- und Transplantationsversuche bei

Lumbriciden. Ber. Zool. Ges., 1898.

=Kowalevski, A. F.=

’72. Über die Vermehrung der Seesterne durch Theilung und

Knospung. Zeit. wiss. Zool., XXII, 1872.

=Krämer, A.=

’47. Über den Palolowurm, 1847.

’99. Palolo untersuchungen. Biol. Centralbl., XIX, 1899.

’99. Palolo untersuchungen in October und November, 1898. _Ibid._

=Krauss, H.=

’98. Selbstverstümmelungen bei den Heuschrecken.

Prometheus, IX, 1898.

=Kroeber, J.=

’00. An Experimental Demonstration of the Regeneration of

the Pharynx of Allolobophora from Endoderm. Biol. Bulletin, II, 1900.

=Lacépède, B. G. E. de.=

1788. Histoire naturelle des quadr. ovip. et des

serpentes. 1788.

=Lang, A.=

’88. Über den Einfluss der festsitzenden Lebensweise auf

die Thiere. Jena, 1888.

=Lefèvre, G.=

’98. Regeneration in Cordylophora. Johns Hopkins

University Circulars, Feb. 8, 1898.

=Lessona, M.=

’69. Sulla reproduzione della parte in multi animali.

Atti della Soc. Ital., X, 1869.

=Lillie, F. R.=

’96. On the Smallest Parts of Stentor capable of

Regeneration. Journ. Morph., XII, 1896.

=Lillie, F. R., and Knowlton, F. P.=

’97. On the Effect of Temperature on the Development of

Animals. Zool. Bulletin, I, 1897.

=Lindemuth, H.=

Über Bildung von Bulben, etc. Ber. bot. Gesell., XIV.

=Loeb, J.=

’91. Untersuchungen zur physiologischen Morphologie der

Tiere. I. Über Heteromorphose. Würzburg, 1891.

’92. Untersuch., etc. II. Organbildung und Wachstum.

Würzburg, 1892.

’92. Investigations in Physiological Morphology. III.

Experiments on Cleavage. Journ. Morph., VII, 1892.

’94. On Some Facts and Principles of Physiological

Morphology. Biol. Lect., Woods Holl, in 1893, 1894.

’94. Über eine einfache Methode, zwei oder mehr

zusammengewachsene Embryonen aus einem Ei hervorzubringen. Pflüger’s

Arch., LV, 1894.

’94. Über die Grenzen der Teilbarkeit der Eisubstanz.

Pflüger’s Arch., LIX, 1894.

’95. Beiträge zur Entwickelungmechanik der aus einem Ei

entstehenden Doppelbildungen. Arch. f. Entw.-mech., I, 1895.

’95. Bemerkungen über Regeneration. Arch. f. Entw.-mech.,

II, 1895.

’96. Über den Einfluss des Lichts auf Organbildung bei

Tieren. Pflüger’s Arch., LXIII, 1896.

’96. Hat das Centralnervensystem einen Einfluss auf die

Vorgänge der Larvenmetamorphose? Arch. f. Entw.-mech., IV, 1896.

’97. Zur Theorie der physiologischen Licht- und

Schwerkraftwirkungen. Pflüger’s Arch., LXVI, 1897.

’98. On Egg-Structure and the Heredity of Instincts.

Monist., VIII, 1898.

’98. Assimilation and Heredity. Monist., VIII, 1898.

’99. Über die angebliche gegenseitige Beeinflussung der

Furchungzellen und die Entstehung der Blastula. Arch. f. Entw.-mech.,

VIII, 1899.

’99. Warum ist die Regeneration kernloser

Protoplasmastücke unmöglich oder erschwert? Arch. f. Entw.-mech., VIII,

1899.

’00. On the Transformation and Regeneration of Organs.

Am. Journ. of Physiol., IV, 1900.

=Loeb, L.=

’97. Über Transplantation von Weisser Haut auf einen

Defect in Schwarzer Haut und umgekehrt am Ohr des Meerschweinchens.

Arch. f. Entw.-mech., VI, 1897.

’98. Über Regeneration des Epithels. Arch. f.

Entw.-mech., VI, 1898.

’99. An Experiment-Study of

Transformation of Epithelium to Connective Tissue. Medicin, 1899.

=McIntosh, W. C.=

’70. Notes on the Development of Lost Parts in the

Nemerteans. Journ. Linn. Soc., X, 1870.

’73-’74. Marine British Annelids. 1873-74.

=Magnus, Albertus.=

1661. Ordinis praedicatorum de animalibus, Lib. XXVI,

tome VI. Lugundi, MDCLI.

=Mall, F. P.=

’96. Reversal of the Intestine. Johns Hopkins Hospital

Reports, I, 1896.

=Marenzeller, F. von.=

’79. Die Aufzucht des Badeschwamms aus Theilstücken.

Verh. Zool.-bot. Ges. Wien., XXXVIII, 1879.

=Martinotti, C.=

’90. Über Hyperplasie und Regeneration der drüsigen

Elemente in Beziehung auf ihre Functionsfähigkeit. Centralbl. f. allg.

Pathol., I, 1890.

=Martins, E. von.=

’66. Über ostasiatische Echinodermen. Archiv. f.

Naturgesch., L, 1866.

’84. Über das Wiedererzeugungsvermögen bei Seesternen.

Sitz. d. Gesell. naturf. Freunde zu Berlin, 1884.

=Mayer, C.=

’59. Reproductionsvermögen und Anatomie der Naiden. Ver.

Nat. Vereins, Rheinlande XVI, 1859.

=Mazza, F.=

’90. Sulla ringenerazione della pinna caudale in alcuni

Pesci. Atti Soc. Ligust. Sc. N., I, 1890.

=Michel, A.=

’98. Recherches sur la régénération chez les Annelides.

Bull. Sc. France et Belg., XXXI, 1898.

=Mingazzini, P.=

’91. Sulla rigenerazione nei Tunicati. Boll. Soc. Napoli,

V, 1891.

=Monti, R.=

’00. Studi Sperimentali sulla Regenerazione nei Rebdoceli

marini. Rendiconti d. R. Inst. Lomb. Sc. e Lett., (Ser. II.) XXXIII,

1900.

’00. La ringenerazione nelle Planarie marine. Mem. R.

Inst. Lomb. Sc. Lett. Cl. Sc. Mat. Nat., XIX, 1900.

=Morgan, T. H.=

’93. Experimental Studies on the Teleost Eggs. Anat.

Anz., VIII, 1893.

’93. Experimental Studies on Echinoderm Eggs. _Ibid._,

IX, 1893.

’95. A Study of Metamerism. Q. J. Micr. Sc., XXXVII, 1895.

’95. The Formation of the Fish Embryo. Jour. Morph., X,

1895.

’95. Half Embryos and Whole Embryos from one of the first

two Blastomeres of the Frog’s Egg. Anat. Anz., X, 1895.

’95. A Study of a Variation in Cleavage. Arch. f.

Entw.-mech., II, 1895.

’95. Studies of the “Partial” Larvae of Sphaerechinus.

_Ibid._, II, 1895.

’95. The Fertilization of non-nucleated Fragments of

Echinoderm-Eggs. _Ibid._, II, 1895.

’96. The Number of Cells in Larvae from Isolated

Blastomeres of Amphioxus. _Ibid._, III, 1896.

’97. Regeneration in Allolobophora foetida. _Ibid._, V,

1897.

’97. The Development of the Frog’s Egg. New York, 1897.

’98. Developmental Mechanics. Science, N. S., VII, 1898.

’98. Experimental Studies of the Regeneration of Planaria

maculata. Arch. f. Entw.-mech., VIII, 1898.

’98. Regeneration and Liability to Injury. Zool.

’99. Regeneration of Tissue

composed of Parts of Two Species. Biol. Bulletin, I, 1899.’99.

Regeneration in the Hydromedusa, Gonionemus vertens. The American

Naturalist, XXXIII, 1899.

’99. A Confirmation of Spallanzani’s Discovery of an

Earthworm regenerating a Tail in place of a Head. Anat. Anz., XV, 1899.

’99. Further Experiments on the Regeneration of Tissue

composed of Parts of Two Species. Biol. Bulletin, I, 1899.

’99. Some Problems of Regeneration. Biological Lectures,

Woods Holl (1898), 1899.

’00. Further Experiments on the Regeneration of the

Appendages of the Hermit-Crab. Anat. Anz., XVII, 1900.

’00. Regeneration: Old and New Interpretations.

Biological Lectures, Woods Holl (1899), 1900.

’00. Regeneration in Bipalium. Arch. f. Entw.-mech., IX,

1900.

’00. Regeneration in Planarians. _Ibid._, X, 1900.

’00. Regeneration in Teleosts. _Ibid._, X, 1900.

’01. Regeneration in Tubularia. _Ibid._, XI, 1901.

’01. The Problem of Development. The International

Monthly, 1901.

’01. The Factors that determine Regeneration in

Antennularia. Biol. Bulletin, II, 1901.’01. Regeneration of

Proportionate Structures in Stentor. Biol. Bulletin, II, 1901.

’01. Regeneration in Planaria lugubris. Arch. f.

Entw.-mech., XII, 1901.

=Morgan, T. H., and Tsuda, Umé.=

’93. The Orientation of the Frog’s Egg. Q. J. Micr. Sc.,

XXXV, 1893.

=Müller, E.=

’96. Über die Regeneration der Augenlinse nach

Extirpation derselben bei Tritonen. Arch. f. mikr. Anat., XLVII, 1896.

=Müller, F.=

’80. Haeckel’s Biogenetische Grundgesetz bei der

Neubildung verlorener Glieder. Kosmos, VIII, 1880-81.

=Müller, E.=

’95. Über das Wiederwachsen (Regeneration) von

Körperteilen. Jahresb. d. Ver. f. vaterl. Naturk. in Württemberg, LVI,

1895.

=Müller, H.=

’64. Über Regeneration der Wirbelsäule und des

Rückenmarkes bei Tritonen und Eidechsen. Frankfurt a. M., 1864.

=Müller, O. F.=

1771. Von Würmern des süssen und salzigen Wassers. 1771.

=Nägeli, C. von.=

’84. Mechanisch-physiologische Theorie der

Abstammungslehre. 1884.

=Newport, G.=

’44. On the Reproduction of Lost Parts in Myriapoda and

Insecta. Phil. Trans., 1844.

=Nussbaum, M.=

’84. Über spontane und künstliche Zellteilung. Sitz. d.

Niederrh. Ges., 1884.

’86. Über die Teilbarkeit der lebendigen Materie. I. Die

spontane und künstliche Teilung der Infusorien. Arch. f. mikr. Anat.,

XXVI, 1886.

’87. Über die Teilbarkeit, etc. II. Beiträge zur

Naturgeschichte des Genus Hydra. Arch. f. mikr. Anat., XXIX, 1887.

’91. Mechanik des Trembleyschen Umstülpungsversuchs.

Arch. f. mikr. Anat., XXXVI, 1891.

’94. Die mit der Entwickelung fortschreitende

Differenzierung der Zellen. Sitz.-Ber. Niederrh. Ges. Bonn, 1894.

=Nussbaum, J., and Sidoriak, S.=

’90. Beiträge zur Kenntnis der Regenerations vorgänge

nach Künstlichen Verletzungen bei älteren Bachforellen embryonen (Salmo

fario. L.). Arch. f. Entw.-mech., X, 1890.

=Parke, H. H.=

’00. Variation and Regulation of Abnormalities in Hydra.

Arch. f. Entw.-mech., X, 1900.

=Parker, G. H., and Burnett, F. L.=

’00. The Reactions of Planarians with and without Eyes to Light. Am. Journ,

Physiol., IV, 1900.

=Parona, C.=

’91. L’Autotomie e la regeneratione delle appendici

dorsale nella Tethys lepornia. Atti della R. Universita di Genova, VII,

1891. (Also Zool. Anz., XIV, 1891.)

=Peebles, Florence.=

’97. Experimental Studies on Hydra. Arch. f. Entw.-mech.,

V, 1897.

’98. The Effect of Temperature on the Regeneration of

Hydra. Zool. Bull., II, 1898.

’00. Experiments in Regeneration and in Grafting of

Hydrozoa. Arch. f. Entw.-mech., X, 1900.

=Perrier, Ed.=

’72. Recherches sur l’Anatomie et la Régénération des

Bras de la Comatula rosacea. Arch. Zool. Expérim., II, 1872.

’73. Sur l’Autotomie et la Régénération des Bras de la

Comatula. Arch. Zool. Expérim., II, 1873.

=Peters, A.=

’89. Über die Regeneration des Endothels der Cornea.

Arch. f. Mikr. Anat., XXXIII, 1889.

=Petrone, A.=

’84. Du processes régénérateur sur le poumon, sur la foie

et sur le rein. Archiv. Ital. d. Biol., V, 1884.

=Pfeffer, W.=

’97. Pflanzenphysiologie, 1897.

=Pflüger, E.=

’77. Die teleologische Mechanik der lebendigen Natur.

Pflüger’s Arch., XV, 1877.

’83, Über der Einfluss der Schwerkraft auf die Teilung

der Zellen. Pflüger’s Arch., XXXI, 1883.

’83. Über den Einfluss der Schwerkraft auf die Teilung

der Zellen und auf die Entwickelung des Embryos. Pflüger’s Arch.,

XXXII, 1883.

’84. Über die Einwirkung der Schwerkraft und anderer

Bedingungen auf die Richtung der Zellteilung. Pflüger’s Arch., XXXIV,

1884.

=Phillipeaux, J. M.=

’66-’67. Experience démontrant que les membres de la

salamandre aquatique (Triton cristatus) ne se régénèrent, etc. Compt.

Rend. d. l’Acad. de Science, 1866-67.

’67. Sur la régénération des membres chez l’Axolotl

(Siren pisciformis). _Ibid._, 1867.

’74. Note sur les résultats de l’extirpation complète

d’un des membres antérieurs sur l’Axolotl et sur la salamandre

aquatique. Gaz. Méd. de Paris, 1874.

’76. Expériences montrant que les mamelons extirpés sur

des jeunes Cochons d’Inde ne se régénèrent point. Compt. Rend., 8 Fev.,

1876.

’76. Les membres de la salamandre aquatique bien extirpés

ne se régénèrent point. Compt. Rend., LXXXII, Nr. 20, 1876.

’79. Note sur la régénération de l’humeure vitrée chez

les animaux vivant, lapins, cochons d’Inde. Gaz. Méd. de Paris, 1879.

’79. Sur la rétablissement de la vue chez les cochons

d’Inde après l’extraction des humeurs vitrée et cristalline. Gaz. Méd.

de Paris, 1879.

’80. Note sur la production de l’oeil chez la salamandre

aquatique. Gaz. Méd. de Paris, 1880.

=Piana, G.=

’94. Ricerche sulla polidactilia acquisita determinata

sperimentale nei tritoni e sulla coda supernumera nelle lucertole. Ric.

Lab. di Anat. norm. di Roma, IV, 1894.

=Pliny, Secundus.=

’77. Secundi historia mundi. Lib. XXXVII, Lib. XI.

=Ponfick, E.=

’90. Über Rekreation der Leber. Verhandl. des X Intern.

Kongresses zu Berlin, II, 1890.

=Porta, Jo. Baptista.=

1650. Neapolitani magiae naturalis libri viginti. Rhotomagi MDCL. Lib. II.

=Prantl, K.=

’74. Untersuch. über die Regeneration des

Vegetations-punktes an Angiospermenwurzeln. Arb. a. d. Bot. Instit. in

Würzburg, IV, 1874.

=Preyer, W.=

’86. Über die Bewegungen der Seesterne. Mitth. Zool.

Stat. Neapol., VII, 1886-87.

=Pringsheim, G.=

’76. Über Vegetative Sprossen der Moosfrüchte.

Monatsberichte d. k. Akad. d. Wiss. zu Berlin, Juli, 1876.

=Przibram, H.=

’96. Regeneration bei den Crustaceen. Zool. Anz., XIX,

1896.

’99. Die Regeneration bei den Crustaceen. Arb. d. Zool.

Inst. in Wien., II, 1899.

’00. Experimentelle Studien über Regeneration. Biol.

Centralbl., XX, 1900.

=Quatrefages, A.=

’65. Histoire naturelle des Annélées. I (page 126), 1865.