610 DEVELOPMENT [CHAP. XLII. 



inches in length. Each body was composed of numerous trans- 

 verse coeca, passing from the Fallopian tube towards the corre- 

 sponding ovary. 



The kidneys are developed independently of the Wolffian bodies, 

 and are situated on the inner side of the ducts of these temporary 

 organs. As the latter gradually diminish in size, the development 

 of the former advances. 



Supra-renal Capsules. The investigations of Mr. Gray upon the 

 development of the supra-renal capsules in the chick, have proved 

 that these bodies are not to be recognised before the end of the 

 7th day, when an ill-defined granular mass, of a reddish color, 

 makes its appearance between the aorta and upper and inner sides 

 of the Wolffian bodies. It seems to have no connexion with the 

 thyroid or thymus, as Professor Goodsir described. Its minute 

 structure resembled that of the spleen about the fifth day of in- 

 cubation. By the 8th day, vesicles could be distinguished, and by 

 the fourteenth day were found to contain oil globules, but no 

 nuclei could be detected in their interior. The capsules were of 

 large size, and of yellow color by the 18th day, and now the 

 division into cortical and medullary portions was quite distinct. 

 The supra-renal capsules are developed from two separate masses 

 of blastema, situated between the aorta and upper and inner 

 extremities of the Wolffian bodies. They have no connexion with 

 the latter, or with each other, and although in their minute struc- 

 ture they resemble the spleen, they arrive at their maximum of 

 development before that organ. 



Organs of Generation. The sexual organs are developed at a 

 later period than other glands. They are formed from masses of 

 blastema situated upon the inner side of the upper and free part 

 of the ducts of the Wolffian bodies. The ovaries and testicles 

 are developed independently of the Wolffian bodies. At an early 

 period of development the glands in both sexes have very similar 

 characters, and it is not possible to say whether the organ is ulti- 

 mately to become converted into a testicle, or whether it is to retain 

 its primitive characters, which agree with those of the ovary. 

 According to the observations of Valentin, the ovary of mammalian 

 animals is developed in the form of tubes, in which the Graafian 

 follicles are produced. 



The excretory ducts in the lowest vertebrata are two in number, 

 and open in the cloaca, an arrangement which is persistent in 

 many fishes, but in the higher classes they are united, and form a 

 single canal, the arrangement of which has been carefully investi- 



