270 
W. M. Wheeler 
regard the Myzostomidae as a peculiar distiuct groiip belonging to 
tlie Annelids, related to the Chaetopods, but also showiug a tendency 
to some of the Arachaids (Liaguatulida, Tardigrada, and perhaps 
Pycnogonida) and Crustaceans«. For the reasons which have induced 
these different aiithors to adopt their respective views I can only 
refer to their papers. 
It will be admitted on all sides* that the structure of the repro- 
ductive Organs and their relations to the coelom äre important dia- 
guostic characters, and it bas been mainly due to a faulty or in- 
sufficient interpretation of these and some other Organs (nephridia, 
parapodia, »siickers«) that some of the most strikingly Chaetopod 
characters of the Myzostomidae have not been generally reeognized. 
It is for the purpose of corroborating the view advanced by Metschni- 
KOFF and helping to establish a permanent resting place for 
this hitherto nomadic group that I subjoin the following consi- 
derations. 
1. The Relations of the reproductive Organs — the testes 
and especially the ovaries — to the body-cavity. The inter- 
pretation of the »Uterus« and »ovaries« of other authors as a 
ramifying body-cavity into which the ova fall and in which they 
grow to their full size, at once recalls the condition seen in the 
Polychaeta. This body-cavity is quite distinct in the youngest My- 
zostomes which I have studied, and its temporary occlusion is due 
simply to an inward growth of the parenchyma in the portion of 
the body ventral to the intestine. This growth appears to be caused 
by the rapid accumulation of male reproductive cells in this regiou 
of the body. When the ova begin to escape from the ovaries the 
body-cavity again reappears and becomes at first coextensive with 
and then more extensive than the superjacent intestinal ramifications. 
The ovaries are merely one, or two [M. cirrife7mm) pairs of thicken- 
ings in the peritoneum lining this body-cavity and may be compared 
without difficulty to the ovaries of Chaetopods. 
The Position of the ovaries in most species of Myzostoma — viz. 
dorsal to the ramifications of the intestine — at first sight appears to 
be a difference of some importance, but species like M. heilig cryi)- 
topoclium and platypus^ where the ovaries are ventral to the branches 
of the intestine, show in this respect a greater resemblance to most 
Chaetopods. The manner in which the young oocytes detach them- 
selves from the ovaries, pass into the body-cavity and there grow 
to their full size, is clearly a Chaetopod character. That they do 
