2JO A. L. TREADWELL. 



degenerate as regards its body wall, muscles and intestine, while 

 the posterior "modified" region shows at least no degeneration 

 of its muscle structure. I am inclined to believe there has been 

 a hypertrophy of these organs, but non-sexual individuals are 

 not available for comparison. Spermatozoa are found all through 

 the body, from the prostomium backward. At no place, however, 

 does the intestine appear as degenerate as in the female. This is 

 especially true of the posterior region, where the intestine is large, 

 filling nearly as much of the coelom as it does in other annelids. 



If the loss of the intestine has arisen in 

 v---.e the female through mechanical reasons, 



connected in any way with the accumu- 

 -tent lation of large numbers of ova around it, 



it is easy to see why the loss should be 



greater in the female than in the male. 

 FIG. 5. Section through Though prese nt in large numbers, the 



head of same individual. 



< 24 . *,eye;*rt,tentacle. spermatozoa would on account of their 



small size, occupy much less room and 



exert much less pressure on surrounding organs, than would 

 the ova. 



Many individuals contained no sex cells, apparently having 

 discharged them into the water. That the sea water must have 

 contained considerable numbers of sex cells is shown by the fact 

 that numbers of spermatozoa are found in the sections, adhering 

 to the body of the female. Fig. 2 represents a number of sperm 

 adhering to the outside of a lobe of the parapodium. 



As shown above, no sex organs were found. It would be of 

 a good deal of interest to know whether they were originally 

 present throughout the body, or are confined to the posterior 

 "modified" end. The latter condition is much the more prob- 

 able. Apparently in this annelid there is, in the heteronereis 

 phase, a considerable degeneration of the anterior " unmodified >: 

 region, the degeneration involving the internal organs and para- 

 podial muscles, though not especially involving the external 

 organs. Into this thin-walled sack thus formed pass the sex- 

 cells, which are now carried in it (as well as in the posterior 

 portions of the body) while the posterior parapodia retain their 

 normal muscular development and function as the main loco- 



