[Illustration:
PTYCHOPTERA PALUDOSA LIMNOBIA REPLICATA
_From enlarged photographs, made at the Yorkshire College,
Leeds, from specimens bred by the Author, and mounted by Messrs.
Watson & Son, High Holborn, London_]
THROUGH
A POCKET LENS
BY
HENRY SCHERREN, F.Z.S.
AUTHOR OF
‘PONDS AND ROCK POOLS,’ ‘A POPULAR HISTORY OF ANIMALS,’ ETC.
_WITH NINETY ILLUSTRATIONS_
THE RELIGIOUS TRACT SOCIETY
56 PATERNOSTER ROW AND 65 ST. PAUL’S CHURCHYARD
1897
Oxford
HORACE HART, PRINTER TO THE UNIVERSITY
CONTENTS
CHAPTER I.
PAGE
THE POCKET LENS, THE DISSECTING MICROSCOPE, AND SOME
SIMPLE APPLIANCES 11
CHAPTER II.
ARTHROPODS AND THEIR CLASSES.--THE MARGINED WATER
BEETLE; THE GREAT WATER BEETLE; THE COCKTAIL
BEETLE 27
CHAPTER III.
COCKROACHES; EARWIGS; THE GREAT GREEN GRASSHOPPER;
THE WATER SCORPION; THE WATER BOATMAN; CORIXA 63
CHAPTER IV.
SPIDERS, MITES, AND MYRIAPODS 96
CHAPTER V.
CRUSTACEANS.--PRAWN, SHRIMP, MYSIS, CRABS; AMPHIPODS;
ISOPODS 128
CHAPTER VI.
AQUATIC INSECT LARVAE 157
INDEX 189
LIST OF ILLUSTRATIONS
FIG. PAGE
_Ptychoptera paludosa. Limnobia replicata_ _Frontispiece_
1. Hand Magnifier and Stand 14
2. Zeiss’s Dissecting Microscope 16
3. Leitz’s Dissecting Microscope 17
4. Two Leitz Lenses in holder (open) 18
5. Two Leitz Lenses in holder (closed) 18
6. Home-made Dissecting Microscope 19
7. Beakers 21
8. Glass Capsule 21
9. Glass Block, with cover 22
10. Glass Box, with cover 22
11. Forceps 23
12. Three forms of Dipping-tube. Method of using it 24
13. Mounted Needles 25
14. Cape Peripatus (natural size) 30
15. Margined Water Beetle (male) 32
16. Shells of Molluscs broken up by Dytiscus 33
17. Outline of Dytiscus 38
18. Male Dytiscus in flight 39
19. To show fold of (right) wing of Dytiscus 40
20. To show fold of (right) wing of Dytiscus 40
21 and 21 A. Head of Dytiscus 42
22. Disposition of mouth parts 43
23. Leg of Cockroach 44
24. Tarsus of Dytiscus (magnified) 45
25. Female Dytiscus swimming 46
26. Upper surface of abdomen of typical Beetle 47
27. Spiracle of Dytiscus (magnified) 48
28. Tracheal tubes of Dytiscus (magnified) 48
29. Great Water Beetle 51
30. Female Hydrophilus constructing a cocoon. (After
Lyonnet) 55
31. Cocktail Beetle 58
32. Cockroaches 66
33. Mouth parts of a Cockroach 69
34. Cockroach, showing Spiracles 71
35. Alimentary Canal of Cockroach 73
36. American Cockroach (male) 75
37. Larva and Pupa of Earwig 77
38. Earwig (male) 78
39. Great Green Grasshopper (female) 81
40. Tibial ear of Great Green Grasshopper 85
41. Land Bug (magnified) 86
42. Water Scorpion 87
43. Organs of Water Scorpion, Egg, and Parasitic Mite.
(After Swammerdam) 90
44. Raptorial leg of Water Scorpion 92
45. Water Boatman 93
46. Water Boatman swimming 94
47. Corixa, with wings expanded 95
48. Scheme of under surface of Wolf Spider (female).
Pedipalp of male (enlarged) 98
49. Garden Spider and Web 99
50. Threads of Spider’s Web 100
51. Anchorage of Web 101
52. Foot of Garden Spider 104
53. Spinnerets of Garden Spider 104
54. Jumping Spider 106
55. Falces of Male Jumping Spider 106
56. Foot of Jumping Spider. Scopula much enlarged 108
57. Diving Spiders 109
58. Cell of Diving Spider 112
59. Red Water Mite 114
60. Larva of Water Mite 117
61. Nymph of Water Mite 117
62. Beetle Mite 119
63. _Lithobius forficatus._ Mouth parts seen from below.
(After Graber) 124
64. The Common Millepede 126
65. Segments of Millepede (magnified) 127
66. Prawn 132
67. First walking leg of Shrimp (enlarged) 134
68. Mysis, or the Opossum Shrimp 135
69. Maxillipedes and Maxilla of Shore Crab. (After
Savigny) 138
70. Stomach of Crab laid open 139
71. Gammarus. (After Sars) 142
72. Maxillipedes of _Gammarus marinus_ (magnified) 146
73. Nest-building Amphipod (from life) 148
74. Water Woodlouse 153
75. Mouth-lock. (After Burgess) 161
76. Dytiscus Larvae 162
77. Pupa of Dytiscus 164
78. Larva of _Limnobia replicata_ 167
79. Forked spine of Limnobia (enlarged) 168
80. Pupa case of Limnobia 169
81. Fore wing of Bee, showing marginal fold (×7) 170
82. Larva of _Paraponyx stratiotata_ (enlarged) 173
83. Diagram of segment of Paraponyx, showing arrangement
of tracheal gills 175
84. Gill of Paraponyx larva. (After De Geer) 176
85. Larva of Sialis (enlarged) 179
86. Diagram of Sialis larva, showing arrangement of gills 181
87. Pupa of Sialis 181
88. Larvae of _Ptychoptera paludosa_ (from life) 184
89. Ptychoptera Larva (enlarged). Tail. (After Lyonnet) 186
90. Pupa of Ptychoptera. (After Lyonnet) 187
THROUGH A POCKET LENS
CHAPTER I
THE POCKET LENS, THE DISSECTING MICROSCOPE,
AND SOME SIMPLE APPLIANCES
The object of this little book is to show how much may be seen
with an ordinary pocket lens, and with a simple microscope; and,
as far as possible, to dispel the idea, far too common, especially
among beginners, that no real work can be done unless one has a
compound microscope, with a large battery of lenses and an array of
‘accessories.’
It would be easy to multiply quotations, from high authorities, in
support of the proposition implied in the foregoing paragraph. Two only
must suffice.
In a recent review of a very good book dealing with Butterflies and
Moths (_Natural Science_, vol. vi. p. 293), the following passage
occurs: ‘The only suggestion we should like to make is that a compound
microscope is unnecessary for any of the details that the author
mentions. A first-rate platyscopic hand lens is much more convenient
and the young naturalist should train himself thoroughly in the use
of it. There is no more common error than the undue use of the higher
powers of a microscope. Except for the intimate details of histology, a
low power or a hand lens is much more easy to use, and its employment
gives a much better idea of the structure.’
The next quotation is of greater interest, as it gives some insight
into the way in which Darwin carried on his investigations. In the
_Life and Letters of Charles Darwin_ (vol. i. pp. 145, 146) we
are told: ‘His natural tendency was to use simple methods and few
instruments. The use of the compound microscope has much increased
since his youth, and this at the expense of the simple one. It strikes
us nowadays as extraordinary that he should have had no compound
microscope when he went his Beagle voyage; but in this he followed
the advice of Robert Brown, who was an authority in such matters. He
always had a great liking for the simple microscope, and maintained
that nowadays it was too much neglected, and that one ought always to
see as much as possible with the simple before taking to the compound
microscope. In one of his letters he speaks on this point, and remarks
that he always suspects the work of a man who never uses the simple
microscope.’
It may be well here to verify the quotations, and also to consult
Darwin’s _Naturalist’s Voyage_, to ascertain what kind of objects
he examined with the simple appliances at his command. In the first
chapter there is an interesting account of a curious limy deposit
on the rocks of the island of St. Paul’s, and of the discoloration
by confervae of the water, which, ‘under a weak lens, seemed as if
covered by chopped bits of hay, with their ends jagged.’ Then we have
an account of the confervae in the Indian Ocean, and of infusoria so
numerous as to tinge the water off the coast of Chile. In the second
chapter we have observations and experiments on planarian worms.
‘Having cut one of them transversely into two nearly equal parts, in
the course of a fortnight both had the shape of perfect animals.’ In
the next chapter he records some observations on the structure of
vitrified tubes formed by lightning striking loose sand. In the fifth
chapter is an elaborate description of a kind of sea-pen; and in the
ninth chapter there are some remarks on the vast number of eggs in the
egg-ribbon of a sea-slug, and on the ‘bird’s-head’ organs in certain
Polyzoa. These remarks were, of course, founded on actual inspection
with the simple microscope.
To this instrument, also, we owe the discovery of the tadpole-like
larvae of Ascidians, or Tunicates, as they are now generally called.
‘At the Falkland Islands I had the satisfaction of seeing, in April,
1833, and therefore some years before any other naturalist, the
locomotive larvae of a compound ascidian.... The tail was about five
times as long as the oblong head, and terminated in a very fine
filament. It was, as sketched by me under a simple microscope, plainly
divided by transverse opaque partitions, which I presume represent the
great cells figured by Kovalevsky. At an early stage of development the
tail was closely coiled round the head of the larva[1].’
* * * * *
We come now to our pocket lens, which may be purchased for a few
shillings of any optician. One can buy a serviceable single lens,
in an ebonite handle, for a shilling; and this cheap instrument is
sufficiently powerful not only to give the worker a good general idea
of the form and structure of objects, but to enable him to do real
work. With it the habits of many of the inmates of his aquaria may
conveniently be watched; he may see their development from stage to
stage of their life-history; and with it, when they are broken up, he
may make out a good deal of their external and internal anatomy.
[Illustration: FIG. 1.--Hand Magnifier and Stand.]
A very good form is shown at Fig. 1, which represents a hand magnifier,
fitted with three lenses of different focus, generally 2 in., 1½
in., and 1 in. Examination of the catalogues of the principal London
opticians shows that such a set of lenses may be bought for about
3_s._ In shape and construction there is sometimes a little
variation; but the form figured is that most generally adopted, and is,
on the whole, fairly convenient. It would, however, be an advantage if
the hole by which the magnifier is mounted on the stand were drilled
in the solid part of the handle. This would not only do away with the
objection that the hole in the case permits dust to penetrate to the
glasses, when carried in the pocket, but would give a longer reach, and
thus obviate the necessity for moving the stand if the observer were
examining a large object. The price of the stand figured is 2_s._
6_d._; and one with a short adjusting arm ought not to cost much
more.
Any one with a mechanical turn may make a stand for himself, though it
may be doubted whether this is quite worth while when these articles
may be bought so cheaply. Nevertheless, there is great pleasure in
making things for oneself; and a home-made stand will enable the
observer to do quite as good work as one that came from the optician’s
shop.
A bill-file weighted at the foot may be bought for a few pence, and
adapted to the purpose. For the slider a large cork cleanly pierced
will answer admirably. This should carry a piece of stout wire, bent
at the end thus __|[image], to serve as a holder for the magnifier,
which should have a hole in the handle, for the reasons stated above.
The only difficulty will be the attachment of the wire to the cork. The
Rev. J. G. Wood advocated winding the wire round the cork in a spiral;
and this is a very good plan. An increase of steadiness is secured, if
a larger cork, or small bung, be used, and the wire inserted in the
side.
There are, of course, more expensive lenses, with which better
definition can be obtained. Zeiss has an excellent magnifier consisting
of two lenses, for use in the dissecting microscope (Fig. 2), and
also as a hand lens, at the price of 6_s._; one of the same
construction, for use in the dissecting microscope alone, may be had
for 4_s._ The Steinheil achromatic lenses are probably the best
of all. These are made in powers ranging from 2 in. to ½ in. focus[2];
and the price varies from 10_s._ up to £1, according to the maker.
Those made by Leitz of Wetzlar cannot be surpassed; and they are sold
in London at 10_s._ each, either mounted in a handle, for use
as hand magnifiers, or with a collar for use in Leitz’s dissecting
microscope (Fig. 3). Mr. Lewis Wright says that ‘the best plan is to
combine both uses, and have two or three powers in collars, with a
spring ring folding into a handle, which will carry any one of them in
that manner. A Steinheil lens at this low price costs little more than
a Coddington, while its performance is infinitely superior[3].’ It is
a difficult thing to get makers to deviate from the beaten track, and
so far as I have been able to learn, Mr. Wright’s wishes have not been
fulfilled.
[Illustration: FIG. 2.--Zeiss’s Dissecting Microscope.]
The lenses and stand (Fig. 1) constitute a simple form of dissecting
microscope. If the worker wishes for something more elaborate, he need
only consult the catalogues of the principal makers to find something
that will meet his requirements. Zeiss’s brass stand, with stage, above
which a lens slides up and down in a holder (Fig. 2), is sold for
9_s._; with blocks for supporting the hands, at 10_s._ It is
a useful instrument for small objects.
My favourite instrument is shown at Fig. 3. Here the focussing of the
lens is effected by rack and pinion work, by means of the screws on
each side the upright pillar. The lens is shown fitted in the collar
which carries it. The stage is of glass--roughly, 2½ in. long by 2
in. wide, and the arm at the top of the pillar can be moved from side
to side, so as to bring a fairly large object within range. The metal
framework of the stage is furnished with nickelled clips (not shown),
which serve to hold an excavated slip. The arm-rests are detachable,
and the uprights are hinged for convenience of packing. The instrument
(with the exception of these rests) packs into a neat, strong mahogany
box, 7½ in. in length, and about 5 in. in height and width. With
two powers--1 in. and ½ in. are very serviceable ones--the cost is
38_s._
[Illustration: FIG. 3.--Leitz’s Dissecting Microscope.]
It is to be wished that the maker would devise some plan by which the
admirable lenses sold with this instrument could be utilized for the
pocket. Mr. C. Curties, of Baker & Co., High Holborn, has kindly done
something in the matter, and has made for me a metal holder. I have
found this convenient, but should be glad to see something further done
in the same direction, so that instrument, lenses, and holder could be
sold for £2. This ought to be within the range of practical optics. The
spring collar advocated by my friend Mr. Wright seems better, and would
certainly be cheaper. The lenses would only need to be dropped in. To
use my pocket holder one must unscrew the metal collar from the lenses
before screwing them into the metal plates which carry them (Fig. 4).
It is, however, something to have made a beginning: it is a step in the
right direction.
[Illustration: FIG. 4.--Two Leitz Lenses in holder
(open).]
[Illustration: FIG. 5.--Two Leitz Lenses in holder
(closed).]
A serviceable dissecting microscope--not a toy, but an instrument with
which real work may be done--can be made at a cost of a few shillings.
Such a one has been made for me by a friend with a positive genius
for such work. The body is fashioned out of a parcel-post box 7 in.
long, 3½ in. in height, and the same in width. From the centre of the
sliding top a piece is cut away, leaving ledges to take a 3 in. by 1
in. excavated slip for small dissections, or a mounted slide of a large
object, such as a whole insect, for examination. A further portion is
cut away on each side to take a small dissecting dish (Fig. 6). To
admit the light, a hole is cut in the side of the box; and the mirror
consists of a piece of silvered glass which was bought of a hawker in
the street. This is placed in the box opposite the square hole, and
sloped at an angle of 45°. The aid of a skilled mechanic was sought
for a small rod carrying a thread, which works in a piece of brass
bent at a right angle. This piece of brass is screwed on the box, just
above the aperture by which light is admitted, and carries a pocket
magnifier, similar to that shown at Fig. 1.
[Illustration: FIG. 6.--Home-made Dissecting Microscope.]
This modest little instrument generally stands on my work-table, and
has provoked some remark and a little good-natured banter from friends
who have seen it. Nevertheless, I should be sorry to part with it, for
I have found it extremely serviceable in many ways. And more than one
critic has had to confess that better results were obtained than one
would expect from its appearance. The total cost out of pocket was,
3_d._ for the box, 3_s._ for the lens, and 1_d._ for the plate-glass,
while the man who made the pillar and ear-piece would take no more
than 6_d._ for his work. This brings the total to 3_s._ 10_d._ With a
little ingenuity the pillar might be made to carry a collar, and so
take a Steinheil lens. This would swell the total cost to about 11_s._
Other apparatus need not be costly. An incident occurred at the meeting
of the Quekett Microscopical Club on November 22, 1878, which shows
how readily common objects may be utilized for our purpose. The late
Right Hon. T. H. Huxley, who was at that time President, exhibited,
and made some remarks on, the dissecting microscope which now bears
his name. During the discussion which followed, Professor Charles
Stewart exhibited some little saucers, which were admirably adapted
for dissecting purposes. The President said that he should ‘be glad
to know where these convenient little saucers could be obtained.’ The
next paragraph of the minutes is interesting and instructive. ‘Mr.
Stewart said they were to be found at the corners of the streets,
containing three whelks or three mussels for a penny. He bought those
he had brought to the meeting at a shop in the New Cut, where they were
supplied to costermongers[4].’
As very many of the objects with which we are concerned are aquatic,
we shall want vessels of some sort to serve as aquaria. Any glass
vessel will answer our purpose, provided it is clear, to allow of the
examination of our captives; or shallow pie-dishes may be utilized.
The glass pots in which preserves are sold will do admirably, and any
glazier will cut us covers for a few pence. Within reasonable limits,
the smaller the aquaria are the better. The inmates can be seen more
easily, and picked out with less trouble when one wishes to examine
them.
The principles on which aquaria should be kept are now pretty generally
understood. There should always be a small quantity of growing aquatic
vegetation, and a supply of minute life to furnish food for the larger
forms. Excess of light should be avoided, and the temperature should
not be allowed to rise much above 50° F. Carnivorous beetles and their
larvae may be fed with small pieces of meat, small garden worms, or
tadpoles. Most of the smaller larvae treated of will be satisfied with
vegetarian diet, varied with an occasional meal of water-fleas.
[Illustration: FIG. 7.--Beakers.]
[Illustration: FIG. 8.--Glass Capsule.]
If one cannot lay the household stores under contribution for jam-pots,
tumblers, and bottles, beakers (Fig. 7) make capital small aquaria.
They are sold in nests, and may be had either rimmed or lipped--rimmed
for choice. There is no difficulty in obtaining them of any optician or
glass-merchant. Mine have been bought from Messrs. Beck, of Cornhill,
as have the capsules, &c., figured here.
Glass capsules (Fig. 8) are made in different sizes, ranging from 1½
in. to 3 in. in diameter, with a height of 1 in. or 2 in. The largest
size, 3 in. by 2 in., costs 5_d._, and a glass circle to cover it,
1_d._ These capsules will be found useful for small aquaria, and
for isolating aquatic larvae in order to keep them under observation
during their change to perfect insects. It was in a capsule of this
kind that some of my Ptychoptera larvae (p. 184) were kept, and changed
into the pupal condition.
The glass block, with cover (Fig. 9), is convenient for a number of
purposes. In it small creatures may be examined in air or in water, and
it makes an exceedingly convenient little dissecting dish for use with
the mounted hand magnifier (Fig. 1), or with Leitz’s stand (Fig. 3), or
the home-made stand (Fig. 6). The glass box, with cover (Fig. 10), is
extremely good for keeping small creatures under observation.
[Illustration: FIG. 9.--Glass Block, with cover.]
[Illustration: FIG. 10.--Glass Box, with cover.]
Excavated glass slips, 3 in. by 1 in., may be bought from any optician.
They serve for the examination of objects in water, and also for
dissection. The best I have been able to get have been supplied by Mr.
J. Hornell, of the Biological Laboratory, Jersey, and they are very
cheap.
We shall need some forceps to pick up specimens from the vessels
in which they are kept, and the same little instruments will be
found convenient in collecting. Both forms have advantages of their
own; if we are limited to one pair, they should be curved, and of
brass. Forceps with ivory tips are very useful for handling aquatic
vegetation. These articles are not usually sold by opticians, but
are kept by the tradesmen in Clerkenwell who sell jewellers’ and
watchmakers’ tools, and cost from 1_s._ to 1_s._ 6_d._ a
pair.
[Illustration: FIG. 11.--Forceps.]
Dipping-tubes are used to take up small aquatic animals from the
vessels in which they are kept. Very little practice will render the
use of this instrument easy. The tube is held firmly between the thumb
and the third and fourth fingers of either hand, while the index finger
is pressed firmly on the top. Most people naturally prefer the right
hand, but it is well to accustom oneself to use the right or left
indifferently. The open end is then put into the water, just over the
object to be secured, and the index finger lifted. The rush of water
into the tube will carry the object into it, and if the finger be again
applied to the top, the pressure of the atmosphere will prevent the
water from escaping when the tube is lifted out[5].
Small brushes are useful for taking up specimens from the water or from
pickle; common ones will do very well for large objects, but for small
objects and parts it is advisable to have one or two sable brushes, as
these form a better point.
Some needles fixed in handles will also be necessary. These may be
bought, or made by fixing ordinary needles of requisite sizes into the
handles sold for small brushes. The needles must be kept free from
rust, and should always be carefully wiped after use. A good plan to
keep them clean is to stick them in a gallipot in which has been
melted a mixture of lard and paraffin in equal proportions.
Small dissecting-knives are useful, but all the work described here may
be done with an ordinary pocket-knife in good trim.
[Illustration: FIG. 12.--Three forms of Dipping-tube.
Method of using it.]
The best preservative for our purpose is formalin, which is sold in
a forty per cent. solution. This should be treated as absolute, and
a five per cent. solution made. This will really be a two per cent.
solution, and is sufficiently strong for general use.
The most profitable use we can make of specimens is to watch their
habits while living, and to break them up and learn as much as we can
about their structure when they are dead. For us to make a collection
of specimens in tubes would be a waste of material.
[Illustration: FIG. 13.--Mounted Needles.]
Little need be said about collecting. The objects treated of are
so plentiful that no great skill, nor any wealth of appliances, is
needed to secure an ample supply. The following remarks on the methods
employed at the Illinois State Laboratory for the capture of aquatic
insects and larvae are, however, worth quoting:--
‘Insects in vegetation, and on or in the bottom, were taken by means of
a dip-net--a net of about equal depth and width attached to a strong
semicircular ring, firmly fixed to a long handle, the straight side of
the ring being opposite the point of attachment. For the larger and
more active forms, a coarser net was used, and for smaller forms one
made of finer net proved most durable and satisfactory. To collect from
the mud of the bottom, the water immediately over it was violently
stirred and then swept with the net. The surface layer of mud was also
scooped up in the fine dip-net, and then allowed to wash through,
leaving the coarser contents in the net. Insects on the bottom in deep
water were secured by using a dredge, and washing its contents through
net sieves. The aquatic vegetation, when free from mud, was violently
washed in a large pan, many smaller forms being thus dislodged and
coming to the surface. Insects occurring in open water were taken in
drawing an ordinary towing-net[6].’
Here we have, so to speak, the general principles of collecting. It
will be easy to adapt them to particular cases.
In choosing the subjects to be treated of in this little book, some
difficulty has been experienced in deciding what to select from the
multitude that lay ready to hand. It was felt necessary that the
subjects should be connected, since choosing them at random would
lead to purposeless work, and so to waste of time and opportunity.
After some consideration, the author has decided to take all the
examples from the Arthrop´oda--that great sub-kingdom of backboneless
animals which includes the Lobster, the Crab, the Sand-hopper and the
Woodlouse, the Spider and the Mite, the whole world of Insects and the
Centipedes. One cogent reason that influenced this decision was the
fact that these objects are exceedingly common, so that there can be no
difficulty in procuring material on which to work. There is, perhaps,
no other sub-kingdom so full of interest, on account of the many widely
different forms, which may be referred to one common plan.
It may possibly appear to some readers that the powers of the pocket
lens have been exaggerated. As a matter of fact the material for the
book has been gathered by actual observation. The author has seen, with
an ordinary pocket lens, the objects here described. If some are shown
as they would appear under greater magnification than such a lens would
give, this is chiefly for the sake of emphasizing points of interest
which might otherwise be overlooked, but which can readily be made out
with a hand magnifier, when attention has been drawn to them, and the
observer knows what to look for.