17 



themselves down to the bottom of the dish. They would then 

 stick together in masses, and beinf; protected from too much 

 pressure by the gelatinous envelope they were found to seg- 

 ment normally. The bunches of eggs were large enough to 

 see with the iinaided eye, and could be easily transferred 

 to the killing fluid, and afterwards stained and cut. The 

 best reagents that were used for killing were corrosive^d«tic 

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

 chloride of mercury; and the full strength (40 per cent.) 

 solution of formalin. Oori-osive-acetic was satisfactory 

 for most purposes, both segmenting eggs and adult medusae 

 being fixed in this solution. They were immersed for from 

 one to ten minutes, according to the bulk of the tissue. 

 Pure (40 X) formalin was used very successfully for the 

 younger stages, giving good cytological fixation of segment" 

 ing eggs and of larvae. Fifteen to forty seconds is suffi- 

 cient to fix the tissues thoroughly. In woi^king with Gon - 

 ionema , I have experienced none of the difficulty that 

 seems to be met with in other coelenterates in getting uni- 

 form results with formalin material. I have used this re- 

 agent not only for fixation but for permanent preservation, 

 with the best results. For narcotizing the larvae and ad- 

 ult medusae, I find menthol crystals the most convenient 



