THE DEVKLOPMENT OF LEPIDOSIREN PARADOXA. 6 



In conclusion I have to record the gratitude which I owe 

 to my friend Mr. J. S. Bndgett for the generous way in 

 which he has placed his store of Protopterus embryos at 

 my disposal. By his kindness I am able to interweave with 

 my description^ references to what takes place in the only 

 other Dipueust still surviving, and consequently to greatly 

 increase its value. 



Methods. 



The eggs and larvas on being brought in from the swamp 

 were first studied alive. For permanent preservation two 

 fluids were used — formalin and alcohol. Of the former 

 solutions in water of from 5 per cent, to 10 per cent, were 

 used, and I found formalin an admirable preservative for 

 the early stages. It caused practically no shrinkage either 

 of capsule or embryo. It further left the former transparent 

 as in the fresh condition. The material of early stages fixed 

 and preserved in formalin was found to be in admirable con- 

 dition, both as to fixation and as to consistency for section 

 work. This, however, only applies to the early and heavily 

 yolk-laden stages. 



The alcohol material was fixed in a variety of ways. 

 Practically all the ordinary fixing agents were tried, but the 

 best all-round results were obtained by corrosive sublimate 

 and acetic acid, and Flemming's chrom-aceto-osmic solution 

 (strong formula). Perenyi's solution proved to be unreliable. 



For section cutting, after many weeks of failure, the fol- 

 lowing three stock methods were adopted : 



I. Thick sections of early eggs, where the cell elements 

 were very large, were cut with a "Jung" microtome after 

 soaking for three days in thin celloidin, three days in thick 

 celloidin, and thirty minutes in chloroform, followed by 

 treatment with cedar oil until clear. The block was kept 

 saturated with cedar oil, and the sections were transferred in 

 order to a shallow ti-ay containing the same fluid. The 

 sections were then arranged upon strips of tissue-paper 

 3 inches by 1 inch within a space equal to the size of the 

 cover-slip used. The paper strips with the sections lying on 



