Memoirs: The Early Development of Julus Terrestris
0
F . 6 0 Mileete M.A, Trinity College
,
Cambridge
By MY investigations, the results of which are contained in the following paper, were begun in June, 1882. I collected a number of Chilognatha and kept them in glass jars, the bottoms of which were covered with damp earth. I soon found that J u l u s t e r r e s t r i s 2 was the species best suited for my purpose, as though the eggs presented some difficulties not present in the eggs of other species, yet they were of a convenient size and were easily to be procured in great numbers. I fed the animals on sliced apples and occasionally on green leaves, and this diet seemed to suit them well, for I never failed to get several clumps of eggs in the breeding season, though it is only this summer that I succeeded in getting them in any number. The breeding season of these animals lasts from the end of May till the end of August, though the weather has a considerable influence on the time when they begin and leave off breeding. I have observed copulation, which takes place exactly as described by Cuvier (cEegne animal/ 3rd edit., 1836, vol. ii, p. 330). I was unable to determine how long a time elapses after copulation before the eggs are laid, but believe it to be short. About four days before laying her eggs the
1 The numbers in brackets in the text refer to the list of papers at the end.
2 The species was kindly identified for me by "Mr. T. D. Gibson Carmichael,
F.L.S., as J u l u s t e r r e s t r i s , Leach.
female constructs a sort of globular case of mud for them. The
bottom of this was, in the case of my animals, formed by the
bottom of the glass, while at the top was a small round hole
which was closed up after the eggs were laid. Four days after
the case was begun the eggs were laid, each case containing a
clump of about a hundred eggs fastened together by a sticky
substance. By breaking away the top of the case I was able
to take out as many eggs as I wanted for examination, and
covering the remainder carefully with earth they proceeded
with their development without injury, though if exposed to
the air for about a quarter of an hour they shrivelled and were
destroyed.
The principal difficulties with which I had to contend in the
preparation of the ova were, in the first place, the hard chitinous
chorion, and, secondly, the great amount of food-yolk.
With regard to the first of these difficulties, I tried to
remove the chorion by Bobretski's method, but I failed
completely in this. I also tried to burst the chorion by endosmosis
of various fluids. Perenny's fluid burst the chorion quickly,
but as soon as the shell was burst in one place the contents
rushed out, destroying the embryo. The state of preservation
of the tissues so preserved was not satisfactory, nevertheless I
gained some valuable series in this manner. I also tried
various strengths of nitric acid with unsatisfactory results. I
was therefore obliged to cut the ova with the chorion still on,
soaking them thoroughly in the hardest paraffine and cutting
rather thick sections. With regard to the preservation of the
tissues I tried a great variety of fluids and also the method of
preserving by heat described by Mr. Patten in his paper (12)
on the development of Phriganids; but I found that I got the
best results from corrosive sublimate, osmic acid, and picric
acid. The last of these fluids, in some cases, burst the shell
after the contents were hardened and thus enabled me to gain
excellent series of sections.
The staining of my sections was a matter of much difficulty.
EAELT DEVELOPMENT OP JULUS TEEEESTBIS.
Borax carmine stained well in the earlier stages, while the ovum
was still in the ovary, and also in later stages, when the embryo
was far advanced in development; but in the intermediate stages,
between about the tenth day and hatching, was wholly useless;
staining the yolk-spherules equally with the nuclei.
Haematoxylin was better, staining the nuclei deeply; but it also
stained the smaller yolk-spherules so as to make it a difficult
matter in some cases to distinguish between them and the
nucleoli. The best fluid was alum-carmine prepared after
Grenacher's method. This fluid has the advantage of staining
the nuclei and nucleoli with a different tinge to that of the
yolk-spherules, and the result was most satisfactory. The
difficulties in the way of observing the course of development were
many and were only overcome by cutting a great number of
sections, only about one series in twenty being perfectly
satisfactory.
The warmth of the weather had a great influence on the rate
of development; one clump of eggs, for instance, was hatched
on the twelfth day after being laid, while another was not
hatched till the twenty-fifth. As the shorter period seemed to
be the most usual, I worked out a clump of eggs which hatched
on the twelfth day, and preserved a number each day, using
the results as a standard by which to estimate the progress of
development in other ova.
I propose in (...truncated)