xiii PHYLUM CHOHDATA 575 



represented in the Pleistocene of South America; the Cerco- 

 pithecidse in the Pliocene and Pleistocene of India by species of 

 the existing genera Macacus, Semnopithecus, and Cynoceplialus, and 

 in the Pliocene of India, France, and Italy by species of extinct 

 genera. Among the Simiidse the Gibbons occur in the Miocene of 

 France and the Pleistocene of Borneo. An extinct genus, Dryo- 

 pithecus, occurring in the Miocene of Europe, is related to the 

 Gorilla ; and a species of Orang (Simia), together with a form 

 allied to the Chimpanzee, occur in the Indian Pliocene. 



The earliest fossil-remains of Man have been found in deposits 

 of Pliocene age in Java ; but though flints of undoubted human 

 manufacture have been found in the Miocene of India, evidences 

 of his existence are extremely rare until we reach the Pleistocene. 



THE MUTUAL RELATIONSHIPS OF THE CHORDATA. 



IN discussing the relationships of the various groups of Chordata, 

 it will be convenient to begin with Fishes, and to work from them 

 upwards and downwards. 



The question of the inter-relationships of the various groups of 

 Fishes is a very puzzling one. As in other cases of the kind, there 

 are three lines of evidence to be kept in mind, anatomical, 

 embryological, and palasontological, the las*t being always, when 

 available, the final court of appeal. 



With regard to anatomical evidence it seems fairly obvious that 

 Fishes having neither limbs nor jaws are more primitive than 

 forms in which those structures are present, unless undoubted 

 evidence of degeneration can be produced: that a purely 

 cartilaginous skeleton is more primitive than a bony one, and a 

 notochord than a vertebral column, however simple ; that a brain 

 with distinct cerebral hemispheres is more advanced than one 

 having an undivided prosencephalon ; that an autostylic skull, 

 being due to the concrescence of originally distinct parts, is more 

 specialised than a hyostylic skull ; that the loss of the spiracle 

 and the presence of an operculum and of a highly differentiated 

 hyoid arch are evidences of specialisation, as also are the presence 

 of air-bladder or lung, spiral valve, conus arteriosus, or copulatory 

 organs. 



In embryology, eggs with much food-yolk are to be looked upon 

 as more modified than those with little, unless there is distinct 

 evidence of reversion towards an alecithal condition. Any special 

 contrivances for the nourishment and protection of the embryo, 

 obviating the necessity for the production of immense numbers of 

 eggs, are also marks of advance. 



On both these lines of evidence the lowest place may safely be 

 assigned to the Cyclostomes. In spite of the similarity of the 



