XXX 



THE MAIN GROUPS OF ANIMALS. 



^^ 



of the Testacea, as compared with animals capable of greater locomo- 

 tion, are furnished by the simplicity of their structure,* which accords 

 with the simplicity of their life, and by the absence, or at any rate the 

 doubtful presence, of the higher_senses, hearing and sight.'^ 



Next above the Testacea come the segmented animals ot Insecta^^ 

 in which group Aristotle included not only Insecta, Myriapoda, and 

 Arachnida, but also intestinal parasites, and in fact all such Annulosa 

 as were known to him, with the exception of Crustacea. 



These were suoerior to the Testacea ; in the first place, because they 

 were capable or t gcomotio n ; secondly, because they had afl ^ the five 

 §fiases ; and thirdly, because they presented generally, though not * in- 

 variably, distinctions of sex, and reproduced their species by congress. 

 They were inferior^'EcTTtie' other two groups of bloodless animals in 

 being occasionally sexless and spontaneously developed ; and in pro- 

 ducing, when sexual, a less perfect generative product, viz. the Scolex. 

 They are therefore distinctly stated by Aristotle to be the coldest of all 

 animals * that give off generative products, that is, of all animals excepting 

 the Testacea. Their low position in the scale was also shown by their 

 want of vital centralisation : for after they have been cut into pieces, 

 each segment continues to live independently for a space, as though 

 the animal were a plant, or an aggregation of distinct animals united 

 into a mass. The only reason, says Aristotle, that such a piece does 

 not live still longer, is that it has not got the necessary organs of 

 nutrition, such as mouth and the like.® _-* 



QLthe two remaining groups of Bloodless animals, the* Crustacea and 

 thcxTephalopods, it is not so easy to decide which was held by Aristotle 

 to be the more perfect. In most respects they were on a par ; for in 

 both the sexes were always distinct, and in both the generative product 

 was an equally immature ovum. Probably, however, the first place must 

 be assigned to the Cephalopods, in virtue of the great size to which 

 they occasionally'' attain, and still more in virtue of their having a 

 brain,* a mark of superiority distinguishing them from all other bloodless 

 animals. 



We come now to Aristotle's second group, the Sanguineous animals, 

 the Vertebrata of Lamarck and his successors. These doubtless from 

 time immemorial have been popularly divided into Beasts, Birds, Reptiles, 

 and Fishes. Aristotle adopted the popular ' division, in the formation 

 of which men had been guided by a happy instinct ; and in so doing 

 he has been followed by all zoologists, until almost in our own day the 

 Amphibia have been separated from the Reptiles, and made to form a 



» D. P. iv. 7, I. 

 * H. A. iv. II, 4. 

 ' H. A. i. 5, 13. 



' H. A. iv. 8, 32. 

 D. G. ii. I, 25. 

 8 D. P. ii. 7, note 9. 



» H. A. iv. 8, 25. 



* D. Juvent. 2, 6, etc. 



» D. P. i. 3, 14. 



