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selves far beyond tlie parapodial insertions into the tbin lateral rim 
of tbe body. Tbere are two pairs of ovaries which are no loDger flat- 
teued bnt of a tiift-like cliaracter. Many of the ova in the body-cavity 
have reached maturity, and in specimens 1.75 mm long the uterus 
(Fig, 5 ut) is often distended with eggs ready to be discharged through 
the uterine oritice [o.ut]. The posterior ends of the nephridia (»ovi- 
ducts« of Nansen) form an nnpaired tube [ne^ph] which opens into the 
anterior end of the cloaca in the midventral line. They do not carry 
olf the ova (unless these be dead and imperfectly developed), as 
Nansen siipposed, but probabiy fimction as excretory Organs. In 
this Stage the testes are fully developed and all, the available inter- 
stices in the parenchyma are stuffed with masses of spermatozoa and 
cells undergoing spermatogenesis. 
Stage 10. 4 mm long. This stage I have not seen, but the 
measurement is given by v. Grafe ('77, pag. 6) and is evidently that 
of mature individuals. For reasons which will be obvious from my 
description of other species, it is highly probable that some in- 
dividuals of this Stage will be found to have the testes, much reduced 
or altogether wanting, and the greater number of the ova nearly or 
quite mature. 
From a consideration of these ten stages it follows: 
1) .that M. cirriferum is virtually hermaphrodite from the begin- 
ning of its sexual development; 
2) that in stages 4 — 8 it is functionally male; 
3) that in stage 9 it is functionally hermaphrodite; 
4) that in stage 10 it is probabiy functionally female. 
It. is evident that this interpretation of the stages briefly de- 
scribed above, with the exception of the first point, may be attained by 
a superficial examination of the different stages, and without tracing 
the ova to their true source in the ovary. But the origin and growth 
of the ovum is of so much importance when we come to examine 
other species or generalize on the sexual phases of the Myzostomidae, 
that it will be necessary to consider the history of the ovum in 
somewhat greater detail. 
And first it must be noted that the emigration of the ova from 
the ovary is not confined to stages 4 and 5, but continues throughout 
the animafs life. Whether there are definite periods of emigration or 
whether there is a continual detachment and emigration of young 
oocytes from the ovary, it is impossible to say, for. although the 
first migration into the empty body-cavity may be readily observed. 
