Portland, Oregon
1922
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Copyright, 1922
by
LAWRENCE E. GRIFFIN
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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 Eugaleus galeus is more frequently named
either Mustelus canis or Galeus canis. The histories of these names and
systematic descriptions of the species are contained in Samuel Garman’s
Monograph 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 mature 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 differences 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 arrangement 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.