MUSEUM OF COMPARATIVE ZOOLOGY. ~ 15 
flame cell, and am thus brought into complete agreement with the results 
obtained by Harmer from Loxosoma. His conclusion (’85, p. 279) that 
the Endoproct nephridium is probably to be regarded as a head kidney, 
like that of Trochophores, seems to me to be justified. A further discus- 
sion of this topic must be deferred till towards the close of this paper. 
The nephridium opens, as already stated, not directly into the vesti- 
bule, but into a pocket of it, the cloaca (Plate III. Fig. 18, Plate IV. 
Fig. 28). The wall of the cloaca consists of a layer of cuboidal epithe- 
lium which is perforated by three openings, —the anus, and the proximal 
openings of the efferent duct and of the vas deferens. 
| The cloaca is an organ which does not occur in any other Endoproct. 
Its existence here is due to the unique position of the rectum and anus, 
and of the opening to the vas deferens. In Loxosoma the last is very 
far removed from the opening of the nephridia. In the Pedicellinide 
the two openings are less distant from each other. In the male of 
P. Benedeni (Fcettinger, ’87, Plate X. Fig. 16), the anus and the open- 
ings of the nephridium and vas deferens are quite near together ; but in 
the female the oviduct of that species opens far distant from the other 
organs. 
Sexual Organs. — Curiously enough, I have not found among all the 
individuals sectioned any ripe females. All the mature individuals of 
the lot collected by me on July 4th from the Schuylkill appear to have 
been males. In no individual did I notice any difference in the position 
of the ducts, such as obtains between the two sexes in Pedicellina Bene- 
deni, — no trace of an incubatory chamber between rectum and the floor 
of the vestibule. 
In the male organs two parts may be distinguished, —testis and vas 
deferens. The testis (Plate IV. Fig. 23) is a paired ovoid body lying be- 
tween rectum, intestine, and the floor of the atrium. In the figure given 
one observes spermatozoa in various stages of development, the wall of 
the sac constituting the germinative epithelium. 
The vas deferens (Plate III. Fig. 18, Plate IV. Fig. 28) is an un- 
paired U-shaped tube, the concavity of the U being turned oralwards. 
The wall consists of a cuboidal epithelium which is ciliated, at least at 
the proximal end of the tube. 
The vas deferens of Urnatella resembles in form that of P. Benedeni 
(Foettinger, ’87, Plate X. Fig. 15), which in turn seems to be more com- 
plicated than that of Ascopodaria. 
Nervous System.—I have been able to make only a superficial study 
of this system. The main ganglion (Plate III. Fig. 18, Plate IV. Figs. 
VOL. XXIv.—Nno. 1. 2 
