600 THE REPRODUCTIVE FUNCTIONS. 



orders of beings, that we perceive no resem- 

 blance in the mechanism employed for their 

 formation. For the purposes of animal life the 

 nutrient j uices must be brought into active circu- 

 lation by means of vessels extensively pervading 

 the system. Nature, then, hastens to prepare 

 this important hydraulic apparatus, without 

 which the work of construction could not pro- 

 ceed. What may be the movements of the 

 transparent nutrient juices at the very earliest 

 period must, of course, remain unknown to us, 

 since we can only follow them by the eye after 

 the nutritive substance they contain has become 

 consolidated in the form of opaque globules. 

 These globules are at first seen to meander 

 through the mass, unconfined by investing ves- 

 sels ; presently, however, a circular vessel is dis- 

 covered, formed by the foldings of the membrane 

 of the embryo, along which the fluids undulate 

 backwards and forwards, without any con- 

 stancy.* A delicate net- work of vessels is next 

 formed in various parts of the area of the circle, 

 which are seen successively to join by the for- 

 mation of communicating branches, and ulti- 

 mately to compose larger trunks, so as to 

 establish a more general system of vascular orga- 

 nization. But increased power for carrying on 



* These phenomena are similar to those which were noticed 

 as presented by the larvse of some insects and other inferior 

 animals. 



