Discovery reports (1954) Discovery reports discoveryreports26inst Year: 1954 ABC D Fig. 4. Ceratias holbulli Kroyer. The esca, A,' Mancalias bifilis', x 18. B, ' Mancalias tentaculatus', xSi. C, Antarctic specimen, x z\. D, Kroyer's type, x \\ (after Gaimard). Waterman attributed to juvenility the smallness of the gonads in his specimen of Gigantactis. The size of the new specimen of Ceratias puts its sexual maturity beyond reasonable doubt (see p. 19), yet in this fish also the gonads are remarkably small. As all the ideas on the sexual dimorphism of these fishes would lead one to expect, t
Discovery reports (1954) Discovery reports discoveryreports26inst Year: 1954 ABC D Fig. 4. Ceratias holbulli Kroyer. The esca, A,' Mancalias bifilis', x 18. B, ' Mancalias tentaculatus', xSi. C, Antarctic specimen, x z\. D, Kroyer's type, x \\ (after Gaimard). Waterman attributed to juvenility the smallness of the gonads in his specimen of Gigantactis. The size of the new specimen of Ceratias puts its sexual maturity beyond reasonable doubt (see p. 19), yet in this fish also the gonads are remarkably small. As all the ideas on the sexual dimorphism of these fishes would lead one to expect, these small gonads are indeed ovaries, and the sex of the specimen is confirmed. But microscopic examination of a teased fragment of the ovary revealed unripe, transparent eggs containing no yolk. Each consisted of a vitelline membrane enclosing a homogeneous cytoplasm which'surrounded a large, central nucleus. The largest ova had diameters up to 16//. The presence of small regressed ovaries, containing eggs in such a young stage of development, suggests a resting condition in an animal characterized by a well-defined and probably short breeding season. If this were general among the Ceratioidea, then it may be supposed that the solitary, sluggish and probably sparsely distributed females might well achieve and pass their sexual season before any free-living males happened to find them. Is it not therefore possible that a severely restricted breeding season may have been a major stimulus leading to the evolution of dwarfed males which become permanently attached to the females? If so, then the suggestion (Regan, 1925a; Parr, 1930, 1932) that the milting of the male may be under direct hormonal control from the female acquires added significance. The ovaries exhibit the cystoarian condition, and are otherwise interesting in that each is strongly bent upon itself into a U-shape within its integument. Each opens separately to the exterior, and the paired genital openings are locate
Size: 1476px × 1355px
Photo credit: © Bookend / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
