Fig. 74.—Pouch with ova, formed by the ventral fins of Solenostoma. Lower aspect; the edges of the fins have been pushed aside to allow of a view of the inside of the pouch. (Natural size.)
The Testicles of the Teleosteans are always paired, and occupy the same position as the ovaries. Their size varies extraordinarily at the different seasons of the year. Vasa deferentia are constant. In the males of viviparous Teleosteans the urogenital papilla is frequently enlarged, and clearly serves as an intromittent organ. In Clinus despicillatus the vas deferens widens within the abdomen into a cavity occupied by a complex network of loose fasciculi, rising from the mucous membrane. The cavity can be compressed by a special powerful muscle, the accumulated semen being thus expelled with considerable force through the narrow aperture of the penis. In many Cyprinodonts the vas deferens runs along the anterior anal rays, which may be thickened, and prolonged into a long slender organ.
Many Teleostei take care of their progeny, but with the exception of Aspredo and Solenostoma, mentioned above (p. 160), it is the male on which this duty devolves. In some, as in Cottus, Gastrosteus, Cyclopterus, Antennarius, Ophiocephalus, Callichthys, the male constructs with more or less skill a nest, and jealously guards the ova deposited in it by the female. The male of some species of Arius carries the ova (Fig. [71]) about with him in his capacious pharynx. The species of Chromis, inhabiting the sea of Galilee, are said to take care of their ova in the same manner. And, finally, in the Lophobranchs, nature has aided this instinct by the development of a pouch on the abdomen or lower side of the tail. In the Syngnathidæ this pouch is formed by a fold of the skin developed from each side of the trunk and tail, the free margins of the fold being firmly united in the median line, whilst the eggs are being hatched in the inside of the pouch. In Hippocampus the pouch is completely closed, with a narrow anterior opening.
Fig. 75.—Syngnathus acus ♂, with sub-caudal pouch.
Fig. 76.—Sub-caudal pouch of Syngnathus acus, with the young, ready to leave the pouch. One side of the membrane of the pouch is pushed aside to admit of a view of its interior. (Natural size.)
The genital organs of Ganoids show similar diversity of structure as those of Teleosteans, but on the whole they approach the Batrachian type. The ovaries are not closed, except in Lepidosiren; all Ganoids possess oviducts. In the Sturgeons the oviduct as well as the vas deferens is represented by a funnel-shaped prolongation of the peritoneum, which communicates with the wide ureter. The inner aperture of the funnel is on a level of the middle of the testicle or ovary, the outer within the ureter; and it is a noteworthy fact that only at certain periods of the life of the fish this outer aperture is found to be open,—at other times the peritoneal funnel appears as a closed blind sac within the ureter. The mode of passage of the semen into the funnel is not known.
In Polypterus and Amia, proper oviducts, with abdominal apertures in about the middle of the abdominal cavity, are developed; they coalesce with the ureters close to the common urogenital aperture.