Stroud, Mammalian Cerebellum. 



75 



A. Macroscopic methods. 



Having obtained an embryo, the first thing to do is to 

 harden it. If the specimen is quite small simply immerse it in 

 50 per cent, alcohol, one to three days ; in 6'j per cent, alcohoi, 

 one to three days ; finally in from 75 per cent, to 80 per cent, 

 alcohol, where it may remain indefinitely. The brain may be 

 exposed at leisure. 



Dissection of Fresh Specimens. — With older embryos where 

 the cartilaginous skull is thick or has begun to ossify, the brain 

 must be exposed at once or it will not harden well. This is a 

 delicate and tedious operation for the young tissues are so soft 

 that when an opening has been made through the skull, a slight 

 pressure upon almost any part of the head will force a consid- 

 erable portion of the brain out through the opening, which of 

 course ruins the specimen. 



The method employed by the writer has been to wrap 

 some absorbent cotton around the body of the embryo and 



