NEW RHABDOCGELE COMMENSAL WITH MODIOLUS 377 
specimen two small, subglobular bodies were seen a short distance 
back of the phar3'nx and laterall}^ placed. These may be testes. 
Female genitalia 
The ovaries are elongated, compact masses of cells b'ing, for 
the most part, lateral and ventral to the intestine. A large part 
of the ovary consists of characteristic cells elongated transversely 
to the length of the organ, with abundant, ver}- fine-grained cyto- 
plasm, and large, clear nuclei with conspicuous nucleoli. These 
cells enlarge, gather a very large amount of A^olk, ultimately be- 
come detached, and are then driven about in the mesenchyme 
by the movements of the worm. Tn horizontal section (figs. 40, 
41) the two ovaries are seen to be continuous on the middle line 
on the ventral side of the intestines with smaller cells which are 
more coarsely granular than the cells of the ovary and have smaller 
nuclei. A duct, traced from the genital pore to the middle of this 
gland, seems to answer to the uterus, but spermatozoa were 
found in it, and, moreover, there appeared to be two ducts in the 
vicinity of the yolk-cells. It is possible that a series of sections of a 
young specimen might show that there is a duct leading from the 
dorsally-placed testes to the sperm-sac. I have not succeeded in 
demonstrating the way in which the spermatozoa reach the sperm- 
sac. It will be noticed from the foregoing account that there 
is some reason for thinking that the cells which are liberated from 
the ovary into the mesenchyme may be fertilized by sperm from 
the sperm-sac, which, if that be the case, would then be a sperm 
receptacle filled from another individual. I find nothing in my 
sections to warrant this conclusion, and nothing in the stained 
and mounted specimens except one curious case of an ovum and 
sperm-sac in close proximity (fig. 38). 
DEVELOPMENT 
Many stages of development, from the large yolk-burdened 
ovum with a single nucleus to the ciliated 3'oung, may be seen at 
the same time in the same adult worm. Some of these forms are 
