mal life, the male is unprotected, while the female is covered by some very perfect shell, or is otherwise well fitted for self-protection, all undoubtedly for the preservation of the young. The higher we ascend in the animal kingdom the more we see the opposite extreme, the male being the best fitted to defend, and hence assuming both its own protection and that of the weaker sex. Far back in remote geological periods animals resembling
Fig. 8.—The Argonaut.
the nautilus and Argonauta were extremely abundant, and also forms even more primitive than these; but to-day we have only a very few as representatives of this large group of fossil animals.
The surface-waters in the Gulf Stream teem with minute life of all kinds. There the young of larger animals exist, microscopic in size; and adult animals which never grow large enough to be plainly visible to the naked eye occur in immense quantities. By dragging a fine silk net behind the vessel, these minute forms are easily taken, and when placed in glass dishes millions uncount-
