450 F. G@. HEATHCOTE. 
female constructs a sort of globular case of mud forthem. 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. 
Methods. 
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 com- 
pletely 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. 
