8 GENERAL PRINCIPLES OF ZOO LOOT. 



nutrition resembling the mammalian and even the human pla- 

 centa; he knew the difference between male and female cephalo- 

 pods, and that the young cuttlefish has a preoral yolk-sac. 



The position which Aristotle took in reference to the classifica- 

 tion of animals is of great interest; he mentions in his writings the 

 very considerable number of about five hundred species. Since he 

 does not mention very well-known forms, like the badger, dragon- 

 fly, etc., we can assume that he knew many more, but did not 

 regard it necessary to give a catalogue of all the forms known to 

 him, and that he mentioned them only if it was necessary to refer 

 to certain physiological or morphological conditions found in them. 



This neglect of the systematic side is further shown in the fact 

 that the great philosopher is satisfied with two systematic cate- 

 gories, with eidos, species or kind, and yeros or group. His 

 eight yevrj juey terra would about correspond with the Classes of 

 modern zoology; they have been the starting-point for all later 

 attempts at classification, and may therefore be enumerated here : 



1. Mammals (CcporoKOvvra ev avrois). 



, 2. Birds (opnOes). 



3. Oviparous quadrupeds (rerpanodoi cooroKovvra). 



4. Fishes 



5. Molluscs 



6. Crustaceans 



7. Insects (errata). 



8. Animals with shells 



Aristotle also noticed the close connexion of the first four 

 groups, since he, without indeed actually carrying out the divi- 

 sion, has contrasted the animals with blood, evai^a (better, 

 animals with red blood), with the bloodless, avai}jia (better, 

 animals with colorless blood or with no blood at all). 



DEVELOPMENT OF SYSTEMATIC ZOOLOGY. 



Pliny. It is a remarkable fact that after the writings of 

 Aristotle, in which classification is much subordinated and only 

 serves to express the anatomical relationships in animals, an 

 exclusively systematic direction should have been taken. This is 

 explicable only when we consider that the mental continuity of 

 investigation was completely broken on the one hand by the 

 decline and ultimate complete collapse of ancient classic civiliza- 

 tion, and on the other by the triumphant advance of Christianity. 



