DISSECTION. 203 



side of the body ; stain and mount a piece, and examine it 

 under the microscope. 



The skin consists of two layers : 



a. The epidermis is a single layer of short columnar 



and somewhat dumb-bell-shaped cells, with a 

 thick cuticle on their outer ends. 



b. The dermis is a very thin layer of connective tissue 



underlying and .supporting the epidermis. It is 

 so thin that it is often difficult to recognise it 

 in specimens treated in this way ; but it will be 

 easily seen in transverse sections of the animal. 



Strip off the myotomes of the right side one by one with 

 needles or fine forceps ; commencing just behind the anus and 

 working forwards until nearly the whole of the myotomes of 

 the right side have been removed, a few only being left at the 

 anterior and posterior ends of the animal. 



In removing a myotome, take hold of its anterior end or 

 angle, and very carefully draw it off backwards, taking care 

 not to pull away the reproductive or other underlying organs. 



3. The notochord is a conspicuous yellow rod traversing 

 the animal from end to end : lying rather nearer the 

 dorsal than the ventral surface, and at the level of 

 the angles of the myotomes. 



L The spinal cord is a white band lying immediately dorsal 

 to the notochord. 



5. The skeleton of the dorsal fin extends along the whole 



length of the dorsal surface except the extreme 

 anterior and posterior ends : it is a firm gelatinous 

 rod, divided transversely into segments which are 

 much more numerous than the myotomes. 



6. The skeleton of the ventral fin is a similar but double 



structure on the ventral surface extending from the 

 atrial pore to the anus. 



7. The reproductive organs are a series of squarish masses 



