Breeding Behavior of the Silverfin Minnow, Notropis whipplii spilopterus (Cope)

Abstract

by the vertebrae), quite contrary to conditions among most other teleosts, in which the posterior boundary of the cavity, in the form of the pectoral arch, is usually suspended from the cranium itself. As a consequence of this development, a greater portion of the gill cover of these eels has also become so far removed from the roots of its normal skeletal supports, in the form of the opercular and branchiostegal ossifications belonging to the general system of the visceral head skeleton, above described, as to render these structures a very ineffective means of support even if they were extended backward over the entire cavity. This fact will be clearly visible from the accompanying illustrations, in which OP, SOP and BR1-5 represent the whole of the normal gill-cover skeleton of teleost fishes. It is, under these circumstances, of course natural to regard the system of the jugostegalia as an adventitious phylogenetic development correlated with the backward expansion of the branchial cavity, and it is quite obvious that a primary expansion of the gill cover would be necessary simply to give room for the parts here considered. Against a positively adaptivistic interpretation may be argued, however, that other eels, e. g. Stilbiscus bahamensis Mowbray, with similarly expanded branchial cavities and inefficient primary skeleton, are doing quite well without the development of any secondary skeletal supports for the gill cover. A more extensive investigation will perhaps increase the number of cases in which jugostegalia are found to be present, but will probably also increase the number of known exceptions. BINGHAM OCEANOGRAPHIC LABORATORY, YALE UNIVERSITY, NEW HAVEN, CONNECTICUT.