. The elasmobranch fishes. Chondrichthyes. THE ELASMOBRANCH FISHES 27 occurrences exceed in lengtli many times the diameter of the body of the cell. From the possession of great numbers of these processes expanded into a com- plex web, the extreme black of a form like Torpedo occidentalis results. The golden cells or lipophores (Ip., fig. 30) (Xanthophores) containing the fatty pigment, lipochrome, are beautifully shown in the young of Heterodon- tiis. Here, with the brown melanophores, they give patches of a warm glossy yellow of remarkable ])eauty. In Cephaloscyllium (fig. 1) also, multitude
. The elasmobranch fishes. Chondrichthyes. THE ELASMOBRANCH FISHES 27 occurrences exceed in lengtli many times the diameter of the body of the cell. From the possession of great numbers of these processes expanded into a com- plex web, the extreme black of a form like Torpedo occidentalis results. The golden cells or lipophores (Ip., fig. 30) (Xanthophores) containing the fatty pigment, lipochrome, are beautifully shown in the young of Heterodon- tiis. Here, with the brown melanophores, they give patches of a warm glossy yellow of remarkable ])eauty. In Cephaloscyllium (fig. 1) also, multitudes of lipophores produce the sulphur spots so characteristic of this form. In Rhino- don (fig. 3) the lipophores associated with reddish brown melanophores form the great orange spots or color patches. In most of the Elasmobranchs, ex- cepting the deep-sea types, pigment cells are absent from the venter. The metallic white here results from the presence of guanin, a waste product of metabolism, which impregnates the cells (leucophores) ventrally as do the pigment granules dorsally. The guanin granules although present are not visi- ble dorsally, for in this location they are obscured by the melanin granules. Ventrally they are very numerous, and have much to do with the production of the light color. Contributing also to the formation of a light-colored venter is a certain concentration of tissues known as argentium. In this concentra- tion the underlying tissues, through the deposition of calcic prisms, become so compact as to form a highly reflecting surface to which the silvery sheen characteristic of a fresh specimen is partly due. The function of pigment has often been thought to be the protection of the more delicate underlying tissues against the rays of the sun. While this per- haps holds in general, such protection from the rays of the sun would not be necessary for those forms like Spinax or Etmopteriis which inhabit the pro- found depths into which the light of the su
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