686 THE GENERATIVE ORGANS. 



he found the gonads in the embryo of Pieris Brassicae as red 

 dots in the dorsal region of the eighth segment of the body 

 right and left of the dorsal vessel. Brandt's description of 

 these bodies in the embryo tallies with Herold's description 

 of them in the caterpillar. Brandt adds, ' In this stage they 

 are elliptical bodies consisting of embryonic cells, with amoeboid 

 nuclei, and are either attached to their ducts by the side or 

 the posterior end ; in the former case they are testes, and in 

 the latter, ovaries.' 



Brandt gives figures representing the several stages of the 

 development of the ovaries and testes from these bodies, which 

 are quite convincing as to their origin. 



Ganin [343] says the sexual organs, in Platygaster, first 

 appear as two rounded cellular masses on each side of the 

 primitive band close to the termination of the digestive tube ; 

 these two masses are united with each other, one elongates 

 and becomes the duct, and the other becomes the gonad. 



Weismann concluded that the rudiments of the gonads 

 make their appearance in the embryo in Musca and Sarcophaga, 

 but he was unsuccessful in discovering them before the larvae 

 had attained the length of a centimetre ; he, however, saw and 

 described them in the newly-hatched larva of Corethra, which, 

 owing to its transparency, is a favourable object for the in- 

 vestigation. 



I have sought for these bodies in both the embryo and 

 larva of the Blow-fly, but have failed to find them either 

 in the embryo or newly-hatched larva. The investigation 

 is one of great difficulty, however, owing to their minute 

 size and the fact that there is no means of recognising them 

 and distinguishing them from other groups of embryonic 

 cells. 



In the larva of about one centimetre in length I have found 

 in sections one or occasionally two pairs of encapsulated groups 

 of small embryonic cells, situated in the fifth abdominal segment 

 imbedded in the fat bodies on either side of, and dorsally to, 

 the alimentary canal, which correspond in general characters 

 and position to rudimentary gonads. The difficulty in my 



