234 
W. M. Wheeler 
selves far beyond the parapodial insertions into tlie tliin lateral rim 
of the body. There are two pairs of ovaries which are no longer flat- 
tened but of a tuft-like character. 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 orifice [o.ut]. The posterior ends of the nephridia (»ovi- 
ducts« of Nansen) form an unpaired tube [neph] which opens into the 
anterior end of the cloaca in the midventral line. They do not carry 
off the ova (unless these be dead and imperfectly developed), as 
Nansen supposed, but probably function 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. Geaff ('77, pag. 6) and is evidenti^ 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 bave 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 virtù al ly hermaphrodite from the begin- 
ning of its sexual development; 
2) that in stages 4 — 8 it is f un et io n all y male; 
3) that in stage 9 it is functionally hermaphrodite; 
4) that in stage 10 it is probably 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, 
4;hat it will be necessary to consider the hi story of the ovum in 
somewhat greater detail. 
And first it must be noted that the e migrati oh of the ova from 
the ovary is not confined to stages 4 and 5, but continues throughout 
the animal's life. Whether there are definite periods of emigration or 
whether there is a continuai 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, 
