The Sexual Phases of Myzostoma. 
285 
rudiniental or obliterateci concomitantly in some cysticolous and 
entoparasitic Myzostomes (e. g. M. piihinar). 
Beard ('84) has given a very different interpretation of the 
male ducts from the above. After attempting* a reduction of the 
oviduet (i. e. the median dorsal opening of the body-cavity) to a 
pair of nephridia, he goes on to say (pag. 566) that the »two male 
ducts are much more easily referable both from position and struc- 
fure to segmentai organs which stili open into the body-cavity«. 
While the reduction of the oviduet to a pair of nephridia hardly 
requires serious consideration, the homology of the male ducts w^ith 
nephridia is not so easily refuted. As Beard himself, however, now 
interprets Nansen's lateral oviducts as nephridia ('94), he would 
probably abandon these earlier homologies, unless, indeed, he should 
assume that two pairs of nephridia bave been retained in the My- 
zostomidae. 
5: Parapodia and Cirri. The resemblance of the cirri and 
parapodia of Myzostoma to the homonymous structures of the Chae- 
topoda has often been pointed out, and I should not bere allude to 
the subject, were it not to cali attention to two structures which 
bave not been sufficiently considered by preceding authors and 
which make the resemblance stili more striking. The first structure 
is the ventral cirrus of the parapodium. This I believe to be 
present in at least two, and possibly in three, species of Myzostoma. 
In M, circinatum the small, pointed and somewhat curled cirri in- 
serted on the inner bases of the parapodia (PI. 10 Fig. 18) are 
in ali probability typical ventral cirri, readily homologized v^ith the 
ventral cirri of Polychaeta. In M. platypus (PI. 11 Fig. 27) the 
heart-shaped elevations with broad bases of attachment are probably 
only another form of ventral cirri, which, curiously enough, seem to 
bave undergone a modification comparable to that of the dorsal cirri 
(elytra) in Chaetopods like Lepidonotus and Tomopteris. I also deem 
it probable that the peculiar pedunculate cups at the bases of the 
parapodia in M. calocotyle^ v. Graff may represent a third form of 
ventral cirri, v. Graff ('84b, PI. 3 Figs. 25 and 26) regarded them as 
»suckers«, but I find it very remarkable that segmentai sacs should 
oceur, not between and some distance dorsal to the parapodia, but 
attached to the bases of the parapodia. Moreover v. Graff figures 
fi ve of these cup-like organs on one side of the body! 
That the twenty cirri which fringe the edge of the disc-like body 
in most Myzostomes are to be regarded as homologues of the 
