202 GENERATION AND DEVELOPMENT. 



females. Aristotle says nothing about such a phenomenon 

 in animals such as those mentioned, but, strange to say, 

 he seems to have believed in the occurrence of a kind 

 of parthenogenesis in mice, for he says that, in some part 

 of Persia, pregnant females are found in the uterus.* 

 This seems to have been a version of a folk-tale to account 

 for the reports current among the Ancients about the 

 amazing rate of increase in the numbers of mice. 



The embryonic development of young animals is dis 

 cussed chiefly in G. A. ii. c. 6, on animals in general, and in 

 H. A. vi. c. 3, on birds. Aristotle also commences H. A. vii. 

 with the intention of describing the development of Man, 

 from the earliest stages of the embryo to old age, but that 

 book is incomplete and contains very little about the subject 

 of development. The so-called Tenth Book of Aristotle s 

 H. A. was believed to be a continuation of Book vii., but 

 it is now admitted that Aristotle did not write it, and, 

 further, on the subject of development it contains nothing 

 of interest. 



The following is a statement of what appear to have 

 been Aristotle s views, as set out in G. A. ii. c. 6, on 

 embryonic development : The upper or anterior parts of 

 the body are generated first, and, except in the Entoma, are 

 proportionally larger than the other parts, the head and eyes 

 being especially large. The larger organs may be seen 

 before the smaller ones, although not necessarily developed 

 before them. In animals with blood, the heart is produced 

 first and blood-vessels extend from it. Then, in order to 

 moderate the heat of the heart, the brain is next formed 

 and also the other parts of the head. The purest parts of 

 the blood pass from the blood-vessels, like water oozing 

 through vessels of partially baked earthenware, and cause 

 the formation of flesh and the main parts of the sense 

 organs. The skin of the body is formed by the drying of 

 the superficial parts of the flesh. From the less pure or 

 more earthy parts of the blood are formed the more earthy 

 parts of the body, e. g., bones, sinews, nails, horns, hoofs, 

 and hair, which are the later formed parts. All the bones 

 are formed in the foetus, and no bones are produced later. 

 About the formation of the eyes there is some uncertainty, 

 he says, but their development is completed at a very late 

 stage. The formation of the bones and sinews is due to the 



* H. A. vi. c. 30, s. 6. 



