1 382.] . Zoology. 511 



quantity diminishes perpetually in energy, and is finally ex- 

 hausted, producing the death of the individual. Meanwhile, cer- 

 tain tracts are set aside as reproductive organs, and produce a 

 fresh supply of this " life-ferment" for the continuance of the spe- 

 cies. The rejuvenescence of the nucleus of the infusoria by con- 

 jugation is homologized with that of the egg by the spermatozoa, 

 but while the nucleoli of the infusoria are principally concerned 

 , the cells which bring about de- 



velopment in the metazoa proceed chiefly from the nucleus of 

 the male sexual cells. 



^ * This is at least an ingenious hypothesis, but lacks support from 

 observation. We know of no " life-ferment," and protoplasm the 

 only life-substance we know of is certainly produced in plants, 

 while animals contain more than they derived from the egg. 



Is Man the Highest Animal? 1 — The measure of zoological 

 rank is the specialization exhibited by all the organs, taken collec- 

 tively. Specialization may be exaggerated in one or several organs, 

 without the animal therefore attaining as a whole a high 'rank. 

 This is the case in man. The measure of specialization is afforded 

 by embryology, which shows in earlier stages the simplicity and 

 uniformity of structure, which in later stages is replaced by com- 

 plexity. The human body preserves several important embryonic 

 features. In man we find three series of high differentiations, 

 namely : in the brain, in the changes induced by or accompany- 

 Mg the upright position, and third in the opposibility of the 

 thumbs to the other digits. These are the principal, though of 

 course not strictly the 'only characteristics of man, which show 

 that he is more specialized than any other animal. In other re- 

 spects he shows a still more striking inferiority. It is of course 

 a familiar observation that his senses are less acute than those of 

 many animals— he has neither the keen vision of the falcon, nor 

 the delicate scent of the dog. He is equally inferior in many 

 structural features. His teeth are of a low mammalian type, as 

 ,s shown both by his dental formula, and by the presen 

 upon the crowns of the teeth, a peculi - 

 ! 11 ' entirely lost in the horse, the 



brutes." His limbs show a similar inferiority since they are 

 . le modified, preserving even the full number of five digits, and 

 »n respect of these members man stands therefore very low, lower 

 tnan the cow and the pig. I [e plants the whole sole of his foot 

 "Pon the ground, yet none except the lower mammalia, together 

 ;^"nnand his - imm ..l, ate cozener, are plantigrade. So too 

 * ltn nis stomach, which is so simple as compared with that of a 

 ruminant, and indeed is of about the same grade as that of the 



ir mvora. It makes, however, a still more forcible impression to 



