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THE POPULAR SCIENCE MONTHLY. 



mal life, the male is unprotected, while the female is covered by- 

 some very perfect shell, or is otherwise well fitted for self -pro- 

 tection, 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- 



