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 nmst 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 Pedicellinida; 

 the two openings are less distant from each other. In the male of 

 P. Benedeni (Foettinger, '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. — NO. 1. 2 



