Note 187 — Chapter X

It may be useful to point out the following examples of parental care among animals in which, as a rule, the eggs are left to take care of themselves. It will be found that in general this instinct is associated with high zoological rank (best exemplified by Mammals and Birds), land or freshwater habitat, reduced number of eggs, and direct development.

Amphibia.—The eggs are sometimes hatched by the male (Alytes obstetricans, Rhinoderma Darwinii), or placed by the male in pouches on the back of the female (Pipa dorsigera, Notodelphis ovifera, Nototrema marsupiatum), or carried during hatching by the female (Polypedates reticulatus).

Fishes.—The Stickleback and others build nests. Of eleven genera of nest-building Fishes, eight are freshwater. The number of eggs is unusually small. Many Siluroids have the eggs hatched in the mouth of the males, a few under the belly of the female. The species are both marine and freshwater, the eggs few and large. Lophobranchiate fishes usually have the eggs hatched by the male. They are marine; the eggs few and large. Many sharks hatch their eggs, which are very few, within the body. Mustelus lævis has a placenta formed out of the yolk-sac.

Insects.—De Geer has described the incubation of the Earwig, and the care of the brood by the female. The cases of the social Hymenoptera, &c., are universally known.

Spiders.—The care of the female spider for her eggs is well known.

Crustaceans.—The Crayfish hatches and subsequently protects her young. Mysis, Diastylis (Cuma), and some Isopods hatch their eggs. Gammarus locusta is followed about by her brood, which shelter beneath her when alarmed. Podocerus capillatus builds a nest among corallines. Several of the Caprellidæ hatch or otherwise protect their young. All these, except the Crayfish, are marine; the eggs commonly fewer than usual.

Echinoderms.—Many cases of “marsupial development” have been recorded in the species of the Southern seas. Here development, contrary to the rule in Echinodermata, is direct.