[Illustration: FIG. 92.--White Surf-fish, viviparous, with young, _Cymatogaster aggregatus_ Gibbons. San Francisco.]
In some viviparous fishes, as in the rockfishes (_Sebastodes_) and rosefishes (_Sebastes_), the young are very minute at birth.
[Illustration: FIG. 93.--_Goodea luitpoldi_ (Steindachner). A viviparous fish from Lake Patzcuaro, Mexico. Family _Pæciliidæ_. (After Meek.)] In others, as the surf-fishes (_Embiotocidæ_), they are relatively large and few in number. In the viviparous sharks, which constitute the majority of the species of living sharks, the young are large at birth and prepared to take care of themselves.
[Illustration: FIG. 94.--Egg of _Callorhynchus antarcticus_, the Bottle-nosed Chimæra. (After Parker and Haswell.)]
The eggs of fishes vary very much in size and form. In those sharks and rays which lay eggs the ova are deposited in a horny egg-case, in color and texture suggesting the kelp in which they are laid. The eggs of the bullhead sharks (_Heterodontus_) are spirally twisted, those of the cat-sharks (_Scyliorhinidæ_) are quadrate with long filaments at the angles. Those of rays are wheelbarrow-shaped with four "handles." One egg-case of a ray may sometimes contain several eggs and develop several young. The eggs of lancelets are small, but those of the hagfishes are large, ovate, with fibres at each side, each with a triple hook at tip. The chimæra has also large egg-cases, oblong in form.
[Illustration: FIG. 95.--Egg of the Hagfish, _Myxine limosa_ Girard, showing threads for attachment. (After Dean.)]
In the higher fishes the eggs are spherical, large or small according to the species, and varying in the firmness of their outer walls. All contain food-yolk from which the embryo in its earlier stages is fed. The eggs of the eel (_Anguilla_) are microscopic. According to Günther 25,000 eggs have been counted in the herring, 155,000 in the lumpfish, 3,500,000 in the halibut, 635,200 in the sturgeon, and 9,344,000 in the cod. Smaller numbers are found in fishes with large ova. The red salmon has about 3500 eggs, the king salmon about 5200. Where an oviduct is present the eggs are often poured out in glutinous masses, as in the bass. When, as in the salmon, there is no oviduct, the eggs lie separate and do not cohere together. It is only with the latter class of fishes, those in which the eggs remain distinct, that artificial impregnation and hatching is practicable. In this regard the value of the salmon and trout is predominant. In some fishes, especially those of elongate form, as the needle-fish (_Tylosurus_), the ovary of but one side is developed.