9 6 



ROSE M. HIGLKY AND HAROLD HI AMI. 



other systems of the body develop to practically tin- same con- 

 dition as in tin- adult, before the gonad makes it> appearance. 

 When the primitive sex cells become recognizable they usually 

 form two groups attached to the anterior external surface of the 

 pericardium from which they appear to be proliferated. Very 

 soon, in rare instances at the time of their formation, these be- 

 come so closely appressed as to appear single though section^ 

 show them to be distinct for a considerable time, frequently alter 

 the gonoducts have formed. Shortly after their appearance a 

 cavity forms within each group, and, with the growth of the 

 gonad, soon becomes more or less triangular. In later stages. 



A 



FIG. i. Gonad and ducts of Trachydermon raymondi. A, section through 

 animal about i mm. long, a, digestive tract; g, gonoduct connecting with gonad; 

 k. kidney; / liver; n, lateral nerve cord; s, shell. B, gonad (o) and ducts in matuie 

 animal, dorsal view. C, reconstruction of same stage a Fig. i. Gonad with 

 ducts ending blindly; kidney showing reno-pericardial and external openings. 



generally about the point of development represented in the 

 figure, these cavities gradually fuse, commencing at the posterior 

 end of the gonad and progressing anteriorly. I n some individual- 

 a slight groove may persist on the ventral surlace between the 

 halves of the gonad for a considerable time, and in a lew case- .1 

 distinct cleft at the anterior end of tin- gland persists until the 

 animal is half grown. 



The aorta holds the normal position on the dorsal surface 

 of the gonad, and there are slight evidences that a portion of 

 the blood it carries makes its way between the halves of the 



