568 BIOLOGY. 



many still retracted into a cloaca, and the testes fre- 

 quently lie within the abdominal cavity. 



3452. As in the tegument the parts separate and 

 each becomes self-substantial, the fibre animal, the tegu- 

 ment vegetal, and so on even in the sexual animal. The 

 ovarium, consisting of two parts, now also separates, since 

 one becomes animal, but the other remains vegetal. The 

 albumen-organ becomes animal, detaches itself from the 

 sexual parts, is developed in the self-substantial tegument 

 and called mamma. 



The Aistheseozoa are thus also Mastozoa or Mam- 

 malia. 



3453. This separation of the sexual animal is one of 

 the first characters. The mammae could never be want- 

 ing, because they indicate an essential stage in the 

 development. The albumen-organ becomes an organ of 

 sensation. If the existence of mammary organs be 

 doubtful, as in the Ornithorynchus, the hairs are in that 

 case perfectly distinct. No Reptile nor Bird can have 

 hairs, because their covering is derived only from a 

 partial system, the respiratory ; while hairs are from the 

 general vascular system, which is the foundation of the 

 tegument, of the sense of feeling. The Ornithorynchus 

 is a furred animal, and this would suffice to bring it 

 among the Aistheseozoa, were we even to deny it mam- 

 mary organs. 



3454. Both sexes, male and female, have breasts. 

 In youth they are most readily detected in the male, 

 because their sexual parts then rank nearer to the female. 

 In other respects the mammae are probably the chiefest 

 organs of absorption for the embryo. 



3455. The mammae are nobler in rank, when, as 

 udders they become self-substantial ; and the more they 

 remove from the belly or abdomen, and come, as breasts, 

 to be placed upon the chest. 



