12 THE AMPHIOXUS. 



study as completely as I possibly could all that is to 

 be seen in the living animal. 



Now it was very evident that the use of reagents 

 was absolutely necessary, and that for several reasons. 

 The constant movement of the ciliated embryos makes 

 the application of reagents which kill them desirable 

 for the purpose of observing the object from every 

 point of view quietly and at one's leisure. This can 

 easily bs clone by carefully moving the cover-slips 

 resting on wax feet, and so turning the dead object 

 without pressing it. In. this way one and the same 

 embryo may be looked at from various sides, and vari- 

 ous optical sections of the same can be got, this being 

 of great importance in. all stages. Further, through 

 the use of reagents many peculiarities of structure 

 stand out more sharply, especially the cellular forma- 

 tion in certain stages ; and thus it is made possible 

 to inspect more satisfactorily the formation of the 

 embryo. 



A third method, and one of great importance, is to 

 cut the embryos into transverse sections. I was not , 

 contented with getting single transverse sections, but 

 as far as possible made unbroken series of them. The 

 great difficulties in my way, when dealing with so 



