The Sexual Phases of Myzostoma. 
237 
with circinate parapodia, but the following differences, some of 
which I believe to be of specific value, may. be pointed out. The 
body of M. wyville-tJiompsoni is only 2.3 mm long and 1.7 mm 
broad. v. Graff's figure shows that the parapodia are relatively 
much larger and provided with more powerful hooks than those of 
circinatum. The most striking difference, however^ is the absence of 
cirri at the bases of the parapodia in v. Gkaff's species. M. %cy- 
tille-thompsoni is from the same locality as my species, but it occurs 
on difFerent hosts, viz. Metacrinus costalis and M. angulatvs. 
The series of sections which was made from the specimen of 
Jf. circinatum revealed a most unsatisfactory histological preser- 
vation. This of course was to be expected in a specimen which 
had lain in alcohol since the days of the Challenger expeditiou. 
Nevertheless it was possible to determine that the structure of the 
reproductive organs was essentially the same as those of M, cirri- 
feriim in stage 9. There were two ovaries on one side of the 
intestine and only one on the other. Probably the single ovary 
originally consisted of two which had become closely applied to 
each other. In minute structure the ovaries agreed in every respect 
with those of cirriferum. The young oocytes could be readily 
distinguished from the deeply staining accessory cells adhering to 
their surfaces. Most of the testicular cells were nearly or quite 
mature, and huge, masses of spermatozoa were found in cavities of 
the parenchyma on either side of the intestine. I was unable to 
find the vesiculae seminales aaid the penes, so that I am in doubt 
as to the manner in which the spermatozoa find their way into the 
water. The testes may, perhaps, dehisce into the body-cavi ty and 
allow the spermatozoa to pass out of the orifice of the uterus. 
3. M. glabrum^ Leuck. 
Like M. cirriferum this species has been repeatedly described 
and figured (Semper '57, v. Graff '77, Beard '84, etc.). It occurs 
on the disc in the immediate vicinity of the mouth of Antedon 
rosacea^^ attaching itself in such a way that its extensible pharynx 
may be inserted into the mouth of its host. Yery frequently the 
larger specimens of M. glahrum bear smaller individuals on the 
1 According to v. Graff ('87 pag. 2) M. glahrum is parasitic also on Ante- 
don petasus, Düb. and Kor. 
