BiOi 

 LIB - 

 Q 



A Guide for the Dissection 

 of the Dogfish 



The small sharks which abound along the coasts of the United 

 States are commonly called "dogfish" by fishermen and others. The 

 "dogfish" of inland waters belongs to an entirely different group. 

 Two species of sharks are caught in numbers and used in laboratory 

 work, the "spiny dogfish" (Squalus acanthias) and the "smooth 

 dogfish" (Eugaleus galeus). The first' is easily distinguished by 

 the sharp spine in front of each dorsal fin. Squalus acanthias is 

 often referred to under the synonym Acanthias vulgaris, while Eu- 

 galeus galeus is more frequently named either Mustelus canis or 

 Galeus canis. The histories of these names and systematic de- 

 scriptions of the species are contained in Samuel Carman's Mono- 

 graph on the Elasmobranchs. 



Several sizes of dogfish are furnished by dealers. We consider 

 it best to purchase large, fully developed specimens. The small 

 specimens may be a little more convenient to handle, but the large 

 ones have the important advantage of being sexually mature, while 

 blood vessels and nerves are dissected better in large than in small 

 specimens. Also, a number of structures are very different in ma- 

 ture animals from their condition in young ones. Dealers should 

 be requested to furnish fish with fins and tails complete instead of 

 trimmed. It is an advantage to issue to the class equal numbers of 

 both sexes. 



An entire specimen and an extra head may be required by each 

 student for a thorough dissection. It would be better if the head 

 were cut off just behind the pectoral fins, instead of in front of them 

 as is usually done, so that the vagus and hypobranchial nerves may 

 be dissected more completely. 



The spiny dogfish, which is the particular subject of this guide, 

 is the species most frequently supplied to laboratories. However, 

 the spiny and smooth dogfishes are so much alike that the latter 

 may be easily dissected with these directions. Where marked differ- 

 ences between the forms exist the structure of Eugaleus is described 

 separately. 



The student of anatomy should realize that dissection is for the 

 purpose of enabling him to see for himself the structures which 

 exist, and that no dissection is satisfactory until the anatomical 

 arrangements mentioned in the text can be completely demonstrated 

 in his specimen. 



The importance of knowing the structure of the elasmobranch 

 is so great in comparative anatomy and embryology that it is worth 

 while to make a thorough dissection of one of this class. As the 

 dogfish is frequently the first major vertebrate form to be studied 

 in detail, these directions have been written to conform to the needs 

 of the student who is beginning comparative anatomy. The arrange- 

 ment of sections in this guide is intended to permit the omission of 

 some which it may not be considered desirable to include in the 

 work of a class. 



48347 



