PEOPLING OF LAND AND SEA 189 



would be degenerate Birds which had lost the faculty of flight 

 as a result of long habitations of regions where no enemy was 

 to be encountered — like the Dodo, which is only a big pigeon, 

 the Penguin and the Auk, related to the Diver. Having 

 abundant food and living in complete security, they acquired 

 considerable proportions, and idly gave up all effort at flight, 

 since flight had become for the time being unnecessary. This 

 renunciation, resulting from the absence of any struggle for 

 existence, proved fatal to them when Man invaded their domain 

 and they could no longer flee from him. 



The Ichthyosauridae were viviparous ; Seps, Slow-worms, 

 Hydrophis, Vipers, and other Reptiles have acquired this 

 character, and there is no a priori reason why certain Birds 

 should have developed it. Perhaps the size of their eggs made 

 a prolonged sojourn in the oviduct difficult, and their lime- 

 producing aptitude evidenced in the compact texture of their 

 osseous tissue, the thickness of the protecting shell of the egg, 

 and the precocity of its formation, were all obstacles to the 

 achievement of viviparity. Be that as it may, the Birds 

 remained oviparous, and all their energ)/ was directed to the 

 construction of nests in which they could lay and sit on their 

 eggs and shelter and warm their young. Their inaptitude for 

 viviparity must be very great, since it has reduced the Cuckoo 

 and the Cow-Bunting or Molobrus, a sort of American Starling, to 

 the expedient of confiding the incubation of their eggs and the 

 rearing of their young to other Birds, in consequence of the 

 disparity between the egg-laying season and the seasonal 

 migration. 



We have now passed in review the conditions in which 

 the principal types, branches, and classes of the Animal 

 Kingdom arose. At the outset, and dominating even the 

 existing evolution of individuals, there is one property 

 fundamental to all living substance — the congregation 

 together in small masses which multiply by division and are 

 capable of association among themselves. The arrangement 

 of these masses or cells is at first regulated by purely 

 mechanical conditions : immobility and mobility determined 

 respectively two main structural types, the branched and the 

 segmented. One of the main divisions of the segmented 

 type, the Annelid Worms, with plastic body, thereupon 



