758 PROCEEDINGS OF THE ACADEMY OF [DeC, 



float in a cloud tlirougli the water, each one surrounded by a very- 

 soft thick gelatinous envelope. If the egg is not fertilized the 

 surrounding mass of semi-fluid jelly slowly shrinks up and the 

 increased specific gravity causes the egg to sink to the bottom. 

 Blister-like vacuoles appear in its substance, puffing out the jelly, 

 and in the course of several days the protoplasm becomes disinte- 

 grated and the egg goes to pieces. 



When fertilization takes place, the shrinking of the egg-envelope 

 is more immediate and greater in degree, so that the egg sinks at 

 once and sticks to the bottom by means of the viscid substance 

 surrounding it. 



Methods. — It may be well to digress at this point in order to 

 mention some of the methods employed in the preparation of 

 material. The adhesive property above referred to is of great 

 assistance in making mounts of the segmenting eggs, as they may 

 be allowed to settle on glass slides, which are afterward run up 

 through all the reagents, without danger of washing off. For sec- 

 tioning, the best way of securing the eggs was found to be by 

 stirring about in the water with a camel' s-hair brush and preventing 

 them from gluing themselves down to the bottom of the dish. They 

 would then stick together in masses, and being protected from too 

 much pressure by the gelatinous covering, they were found to seg- 

 ment normally. The bunches of eggs wei'e large euougli to see 

 with the unaided eye, and could be easily transferred to the killing 

 fluid, and afterward stained and cut. 



The best reagents that were used for killing were corrosive-acetic, 

 three per cent, glacial-acetic in saturate solution of bichloride of 

 mercury, and the full strength (forty per cent. ) solution of forma- 

 lin. Corrosive-acetic was satisfactory^ for most purposes, both 

 segmenting eggs and adult medusse being fixed in this mixture. 

 They were immersed for from one to ten minutes, according to the 

 bulk of the tissues. Pure (forty per cent. ) formalin was used 

 very successful!}^ for the younger stages, giving good cytological 

 fixation of segmenting eggs and of larvse. Fifteen to forty 

 seconds is sufficient to fix the tissues thoroughly. In working with 

 Gonionema I hav^e experienced none of the difficulty that seems to 

 be met with in other coelenterates in getting uniform results with 

 formalin material. I have used this reagent, both for fixation and 

 for permanent preservation, with the best results. For narcotizing 



