220 p. G. HEATHOOTE. 



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. Pour 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 diflficulties, 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 Phryganids ; 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 difHculty. 



