110 PRIMITIVE ANIMALS 



The origin of the skeletal characters of the 

 Mammalia and of their teeth in fact, of all those 

 hard parts which are capable of being preserved in 

 fossilized remains is clearly indicated to us in a 

 group of ancient and extinct Reptiles, the Anomo- 

 dontia, which flourished in the Secondary period. 

 Their remains have been found in Triassic strata in 

 widely separated parts of the earth, viz. in S. Africa, 

 in Scotland and in Eastern Europe, and they afford 

 a beautifully clear transition from the reptilian to the 

 mammalian type of structure. These Anomodont 

 Reptiles had not only acquired the essential characters 

 of the mammalian skeleton and teeth, but they had 

 branched out into various forms, in accordance with 

 various modes of life, which simulate remarkably the 

 divergent groups of modern Mammals, e.g. some were 

 carnivorous, others herbivorous, others insectivorous, 

 and these several habits have left their indubitable 

 mark, especially on the characters of the teeth in 

 these early mammalian ancestors. But on internal 

 structure and mode of reproduction these fossils 

 throw little if any light. 



It is a very familiar fact that Birds and Reptiles 

 lay eggs, that these eggs are incubated either by the 

 parents or by the action of the sun or the heat en- 

 gendered by the fermentation of decaying vegetable 

 matter, and that from the eggs the young emerge 

 and may straightway care for themselves, or, especially 



