HANDLES : ANATOMY OF ACAVUS. Ill 



a large structure pouring its secretion into the hermaphrodite duct 

 hy two separate openings. On leaving the albumen gland the 

 hermaphrodite duct becomes enormously dilated, and is divided into 

 a thick- walled glandular prostatic portion {pr.) and a thinner- walled 

 distensible portion, the oviduct {ov.d.) ; the former communicates with 

 a slightly coiled vas-deferens (v.d.), which enters the penis on its 

 posterior end, a little above the insertion of the retractor muscle. 

 The oviduct is then continued on into the vagina {v.g.) and receives 

 the opening of a very short-stalked spermatheca {sp.). There is 

 hardly any trace of an atrium ; the penis and vagina, though com- 

 municating with a common genital opening, scarcely fuse to form 

 a common genital cloaca. 



The structure of the penis, as before mentioned, is of particular 

 interest, inasmuch as the various species of Acavus present appre- 

 ciable differences with respect to its internal organization. Taking 

 A. hcemastomus as a type (PI. IX, Fig. 12), we find, on opening the 

 penis along the mid-dorsal line, two large lateral pilasters {pi.), having 

 their surfaces ridged and corrugated ; lying between these folds is 

 a conspicuous furrow bounded by two tumid lips. The two pilasters 

 converge towards the anterior end of the penis, and in this region 

 a thickening of the ventral wall {v.t.) of the penis is noticeable; this 

 swelling is better developed in other species. 



At the posterior end of the penis is a large penis-papilla {pp.), 

 at the base of which the vas-deferens opens. 



In A. phoenix (Fig. 13) three pilasters are present, there being 

 a median dorsal one in addition to the two lateral ones. The penis- 

 papilla is also much smaller than in the preceding type. 



Acavus superbus (Fig. 14) presents a somewhat different structure. 

 There arc no definite pilasters, but rather a series of lateral 

 longitudinal ridges which are markedly papillate. The median 

 thickening of the ventral wall of the penis, that was apparent in 

 A. hcemastomus, becomes excessively developed here, and partially 

 overlies the median furrow. The penis-papilla is very small. The 

 penis in A. superbus is, relatively to the size of the animal, much 

 smaller than in either A. hcemastomus or A. phoenix. 



Equally well-marked differences are observable in the internal 

 structure of the penis of A. Waltoni and that of A. Polcii. In the 

 former (Fig. 15) the walls are beset by longitudinal ridges with 

 a corrugated appearance; there is no definite _ aggregation of these 

 folds into pilasters, and the penis-papilla is not very conspicuous. 

 This structure approximates most closely to the condition shown in 

 A. phoenix, whereas the structure of the penis of A. Pole ii more nearly 

 approaches that of A. hcemastomus. 



In A. Poleii (Fig. 16) there are two well-marked lateral pilasters, 

 which converge towards the anterior end of the penis ; here the 

 median ventral thickening becomes very conspicuous, and forms 

 a thickened ridge. The penis-papilla {p.p.) is also of excessive size. 



The penis of A. SMnneri was too small, and not sufficiently well 

 preserved, to make out accurately the characters of its internal 

 structure. 



