A Guide for the Dissection
of the Dogfish
The small sharks which abound along the coasts of the UnitedStates 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 laboratorywork, the “spiny dogfish” (Squalus acanthias) and the “smoothdogfish” (Eugaleus galeus). The first is easily distinguished bythe sharp spine in front of each dorsal fin. Squalus acanthias isoften referred to under the synonym Acanthias vulgaris, while Eugaleusgaleus is more frequently named either Mustelus canis orGaleus canis. The histories of these names and systematic descriptionsof the species are contained in Samuel Garman’s Monographon the Elasmobranchs.
Several sizes of dogfish are furnished by dealers. We considerit best to purchase large, fully developed specimens. The smallspecimens may be a little more convenient to handle, but the largeones have the important advantage of being sexually mature, whileblood vessels and nerves are dissected better in large than in smallspecimens. Also, a number of structures are very different in matureanimals from their condition in young ones. Dealers shouldbe requested to furnish fish with fins and tails complete instead oftrimmed. It is an advantage to issue to the class equal numbers ofboth sexes.
An entire specimen and an extra head may be required by eachstudent for a thorough dissection. It would be better if the headwere cut off just behind the pectoral fins, instead of in front of themas is usually done, so that the vagus and hypobranchial nerves maybe 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 lattermay be easily dissected with these directions. Where marked differencesbetween the forms exist the structure of Eugaleus is describedseparately.
The student of anatomy should realize that dissection is for thepurpose of enabling him to see for himself the structures whichexist, and that no dissection is satisfactory until the anatomicalarrangements mentioned in the text can be completely demonstratedin his specimen.
The importance of knowing the structure of the elasmobranchis so great in comparative anatomy and embryology that it is worthwhile to make a thorough dissection of one of this class. As thedogfish is frequently the first major vertebrate form to be studiedin detail, these directions have been written to conform to the needsof the