192 THE SCIENTIFIC MONTHLY
is an indication that Bome individuals are beginning to put a small amount of choice into this service. In the solitary wasps> typified by Ammophila^ individuals of the same species differ greatly in the amount of food they furnish their young. Some are good providers, others poor. Some also are exact and precise in all their movements, others are very negligent and disorderly, leaving their offspring less effectively pro- tected in numerous ways.
There is similarly a high degree of difference among iodividuals of the same species in the vertebrate line from fish up to man in the amount and efSciency of voluntaiy service to offspring. Some sunfish, for example, will fight courageously to protect their rude nests, others are very timid. Some birds, though trembling with fright, will continue to sit upon and protect their eggs even when threatened with death, while other individuals of the same species desert their ^gs or young upon the least approach of danger. The lower races of man, likewise, show their inferior stage of development most forcibly in the insufBcient food and care they give to wife and children.
As we glance backward over the history of the earth from the present Cenozoic Era, through the Mesozoic and Paleozoic, we see that compul- sory srvice was ever present; that many millions of years ago in the lowest Paleozoic the grosser kinds alone existed; that gradually through the succeeding ages higher types of compulsory service appeared, existing side by side with the grosser; that, finally, voluntary service evolved, and, developing very slowly, reached a degree worthy of the name only in the Cenozoic. These various types of service continued to exist side by side; and since it was the more highly evolved plant or animal group that exhibited the correspondingly high type of service these occupied the better regions of the earth, forcing the less highly developed to less desirable habitats.
That the consumption of other organisms for the prolongation of one's own life extends from the present to the early periods of earth history not only the testimony of tooth structure, claws, tentacles and other food-capturing organs testify, but a multitude of actual records prove. Skeletons of marine reptiles (Plesiosaurs) are abundant in the Mesozoic era, which show in the region of the body where the stomach was formerly situated, the erushed cells of pelecypods and ammonites, the internal skeletons of squids and the broken bones of flying reptiles. In the Hving chamber of fossil cephalopods also occur at times the hard shell and scale remnants of the diet of these animals; these are found from the lower Paleozoic to the present. The appearance of fish scales in the living chamber of lower Paleozoic individuals testifies to the welcome they gave the earliest fishes upon this earth.
Besides this gross type of compulsory service there was present by
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