THE REPTILE-LIKE BIRD. 227 



Mammals, are still scarcely distinguishable from those of 

 Tortoises and other Reptiles. The cleavage of the yolk is 

 partial in the case of Birds and Reptiles, in Mammals it is 

 total. The red blood-cells of the former possess a kernel, 

 those of the latter do not. The hair of Mammals develops 

 in closed follicles in the skin, but the feathers of birds and 

 also the scales of reptiles develop in hillocks on the skin. 

 The lower jaw of the latter is much more complicated than 

 that of Mammals ; the latter do not possess the quadrate 

 bone of the former. Whereas in Mammals (as in the case of 

 Amphibia) the connection between the skull and the first 

 neck vertebra is formed by two knobbed joints, or condyles, 

 in Birds and Reptiles these have become united into a single 

 condyle. The two last classes may therefore justly be united 

 into one group as Monocondylia, and contrasted to Mammals, 

 or Dicondylia. 



The deviation of Birds from Reptiles, in any case, first 

 took place in the mesolithic epoch, and this moreover 

 probably during the Trias. The oldest fossil remains of 

 birds are found in the upper Jura (Archfeopteryx). But 

 there existed, even in the Trias period, different Saurians 

 (Anomodonta) which in many respects seem to form the 

 transition from the Tocosauria to the primary ancestors of 

 Birds, the hypothetical Tocornithes. Probably these Tocor- 

 nithes were • scarcely distinguishable from other beaked 

 lizards in the system, and were closely related to the 

 kangaroo-like Compsognathus from the Jura of Solenhofen. 

 Huxley classes the latter with the Dinosauria, and believes 

 them to be the nearest relations to the Tocornithes. 



The great majority of Birds — in spite of all the variety in 

 the colouring of their beautiful feathery dress, and in the 



