PAET I. 



DIRECTIONS FOR LABORATORY WORK. 



EMBRYO DOGFISH (Acanthias). 



Material. For each student a specimen of the late embryo 

 of Acanthias, known to the fishermen as ' dog-fish pups. ' This 

 should have at least the arterial system injected (easiest done 

 by partly cutting off tail behind last dorsal fin and injecting 

 the caudal artery). 



One or more slides of the skin of the ' pup. ' These may 

 be prepared an hour or more before the laboratory period 

 by placing a bit of the skin on a microscopic slide in a drop 

 of glycerine and covering it with a bit of cover-glass. Such 

 preparations are but temporary; permanent mounts which 

 can be used year after }^ear may be made as follows : The piece 

 of skin, | inch square, is placed for 30 minutes in each 959^ and 

 absolute alcohols and then in spirits of turpentine. It is then 

 placed for a moment on a bit of filter-paper to remove the 

 superfluous turpentine, placed in a drop of balsam" on the 

 slide and the cover-glass applied. Another slide of the decal- 

 cified skin stained and cut in sections will show other features 

 of the scales. 



GENERAL TOPOGRAPHY. Distinguish in the fish anterior 

 and posterior, right and left, back (dorswri) and belly 

 (venter). Is the animal bilaterally symmetrical? i.e., 



are the right and left sides alike? Do you recall any 



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