cxxii. Proceedings. 



VI. Epizoa... ... ... ... Fleas, Bugs, Ticks, 



Lice, &c. 

 VII. A miscellaneous group ranging from Cynipidae to 

 Tineina. 

 VIII. Julus and Scolopendra ... Centipedes, Millipedes, 



Wood-lice, &c. 

 IX. Spiders and Scorpions. 

 X. Helminthes ... ... ... Tape Worms and 



Thread Worms. 



MOLLUSCA. 



These are grouped as follows : — 



I. Without Shells, fixed ... Sponge, SeaAnemones, 



Sea Nettles, and Sea 

 Acorns. 

 II. Without Shells, not fixed ... Sea Cucumbers, &c. 



III. Tethyon, a solitary representative of the Ascidia. 



IV. Star fishes. 



V. Echini or Sea urchins. 

 VI. Shell-fish, viz. : — a, Univalves ; 6, Bivalves; c. Spirals. 



Under these heads Aristotle describes or mentions some 400 

 species of Animals. 



In addition to the classification and description of particular 

 forms, Aristotle may also claim the credit of being the first 

 known writer acquainted with some of the main principles of 

 comparative physiology, e.g. he distinguishes the various 

 tissues, and recognises homological relations. In regard to 

 human anatomy, however, his knowledge is very defective. 

 He is aware of the existence of an optic nerve, but denies any 

 connexion between the brain and the ear ; though he is 

 acquainted with the Eustachian tube. His notions of the 

 circulation of the blood and of the processes of digestion are 

 of the vaguest kind, nor does he clearly distinguish between 

 excretion and secretion. He knows the windpipe and its 

 bifurcation, is aware that it communicates with the lungs ; but 

 has an entirely erroneous conception of the process of re- 

 spiration, imagining the heart to be filled with air. He mentions 

 the most important organs, but has no clear notion of their 

 functions. Among Aristotle's more important errors in com- 

 parative and descriptive anatomy, are his confusion of the 

 knee and the heel in the horse, and his statement that the 

 lion's neck consists of a single bone and has no marrow. 

 He describes at considerable length and with much detail 

 the development of the chick in the egg, which he had 

 evidently attentively watched, and particularises the germ of 

 the embryo, the yolk, the albumen, the allantois, and the 

 amnion, in language which is substantially correct though 

 there are errors in detail. 



