1895.] NATURAL SCIENCES OF PHILADELPHIA. 259 



fecundity. In consequence their danger of extinction through the 

 destruction of their eggs was correspondingly increased. 



In review of what is above said, it may be remarked that in the 

 early days of reptilian dominance, and of general lack of animal 

 activity and intelligence, the reptilian lords of the earth were exposed 

 to little danger of being devoured in the egg by hungry enemies, and 

 needed little care for eggs and young; the result being that no very 

 marked instinct of concealment or personal supervision became de- 

 veloped. But during the later Mesozoic period, an important change 

 took place in the situation. Ages before the reptiles lost their domi- 

 nance a new order of beings, the mammals, had come into existence. 

 The ancestors of the mammalia — typified by the modern Ornithorhyn- 

 chus — were themselves egg-layers. Marsupial mammals followed, 

 and continued throughout most of the Mesozoic age. Insignificant 

 in size, and probably as lacking in intelligence as their reptilian 

 competitors, these creatures long contented themselves with gleaning 

 after the great reptiles, with no evidence of ability to compete with 

 them. Finally appeared the placental mammals, whose young were 

 at birth able to take care of themselves. And, with the coming of 

 this animal type the prevailing stupidity began to yield to a mental 

 condition a step nearer intelligence. 



The reptiles had hitherto occupied the field, the mammals being 

 helpless against them by any direct methods of assault, while the 

 greater activity of the latter, and the consumption of the bulk of the 

 food supply by the great reptiles, checked any disposition in the 

 mammals to increase in size. It is not unlikely that the newcomers 

 gained the victory at length by the indirect methods indicated, an 

 assault upon the eggs, and perhaps the young, of their powerful rivals. 



It is highly probable that the placental mammals, with slowly de- 

 veloping intelligence, adopted, from time to time, new methods of 

 attack; while the reptiles, depending mainly upon previously ac- 

 quired instincts, were very much slower in developing new methods 

 of defence. The reptiles, therefore, eventually found themselves at 

 a serious disadvantage in competition with their small, active', and 

 more cunning opponents. Contemporaneous with the great reptiles 

 were multitudes of prowling creatures, small and agile, whose grow- 

 ing mental powers gradually made them aware that reptilian eggs 

 were full of savory nutriment, and in time taught them the simple 

 arts of concealment of the sea monsters, and how to circumvent the 

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