GENEEATION AND DEVELOPMENT. 203 



abstraction of moisture from the less pure parts of the 

 blood, by means of the internal heat. 



Many of these views are incorrect, but they are evidently 

 based on actual dissection or inspection of embryos in one 

 or more animals. It M^ill be sufficient, however, to state 

 that the cerebro-spinal axis is one of the first parts to be 

 laid down, and that the parts of the body are not developed 

 in succession in the way Aristotle seems to have believed. 

 Many parts, e. g., the flesh, bones (first laid down as 

 cartilages), sinews, skin, sensory organs, heart, alimentary 

 canal, and liver, are in process of development simultaneous- 

 ly. He knew nothing about the formation of membrane 

 bones or the process of ossification of cartilages. It is quite 

 true that, as Aristotle says, the eyes are completed at a late 

 stage of embryonic development. 



His most interesting embryological research is that on 

 the development of a chicken. This research alone entitles 

 him to considerable credit as an original investigator. 

 It is difficult to follow some parts of his description, in 

 H. A. vi. c. 3, not only because of apparent defects in the 

 Greek text, but also because Aristotle gives only a few 

 definite statements about the times of incubation at which 

 the appearances to which he refers were seen. 



One question on which Aristotle's opinion would be of 

 interest relates to the position of the part of the egg in 

 which development begins. His statements on this question 

 are not as clear as could be wished, but it seems that he 

 believed that the part referred to was in the pointed end of 

 the egg. In a passage, the full meaning of which is not 

 clear, he speaks of a movement of the yolk or a part of it 

 towards the pointed end (o|y) of the egg, where, he says, is 

 the beginning (a^x"^) of the egg.* 



He seems to have been misled by assuming that an egg 

 issues from the parent in a manner different from the way 

 in which a young mammal comes to light, for he says that 

 the foot end, as it were, of the egg issues first, whereas the 

 head or beginning (o^px^) of a young viviparous quadruped 

 first comes to light, t He knew also that the broad end of 

 the egg leads during the process of laying. + It was natural, 

 therefore, for him to conclude that the pointed end was the 

 beginning of the egg. His error will not appear to be 

 extravagant if it is borne in mind that Hieron. Fabricius 



- H. A. vi. c. 3, s. 1. f O. A. iii. c. 2, 752&. 



I H. A. vi. c. 2, s. 2 G. A. iii. c. 2. 752a. 



