8 C. S. MINOT ON DISTOMUM 



The testes are of unequal size and asymmetrically placed (fig. 5), as I have already 

 mentioned. They are surrounded by a fibrous membrane just like that which encloses 

 each sexual gland in the Planarians, 1 and forming a complete envelope. This membrane is 

 continued on to the efferent duct (fig. 13, d, e), which is a small tube. Neither within 

 this tube nor within the testicular capsule, have I been able to discover any traces of a 

 lining epithelium. The contents of the testicles are cells, and spermatozoa both ripe and in 

 various stages of development, but all irregularly distributed, producing such confusion 

 that the exact development of the spermatozoa cannot be followed. I could only make 

 out that the heads are developed out of the nuclei of the parent cells. 



The efferent ducats run towards the penis bulb, into which they of course open, though 

 I have not seen the communication. The penis bulb is really the fixed basal portion of the 

 penis. Its walls, as seen in transverse section, fig. 4, A, are very thick, and marked off 

 both internally and externally by a thin membrane, whose appearance recalls the basement 

 membrane of the body. The rest of the wall between the limiting layers consists mainly 

 of rounded cells each containing a nucleus, but with their remaining histological characters 

 nearly obliterated in all my preparations. The cavity of the bulb contains a mass which 

 I suppose to be the coagulated sperm, but no evidences of an epithelial lining are visible, 

 nor can any distinct muscular fibres in the wall of the bulb be seen, though usually they 

 are highly developed in Plathelminths. 



The general shape of the penis and its bulb may be best seen in fig. 11, which repre- 

 sents a longitudinal section. The penis proper is seen to rise almost perpendicularly at 

 first, and then curving around backwards to gradually enlarge, passing over into the bulb 

 without any sharp line of demarcation. I could not make out the distribution of the 

 muscles in the penis on account of the numerous cells, apparently glandular, whose large, 

 dark stained nuclei are very noticeable. The canal is not straight, but undulatory in its 

 course. I am quite sure there is no flagellum. The penis bulb is the same organ that 

 Moseley 2 calls the Prostata in Planarians, and corresponds to the Cirrhusbeutel of the Ces- 

 tods. I have in my previous papers already noticed the exact homologies which may be 

 traced in the male organs of Plathelminths, and in D. crassicolle we find the same parts : 

 1, testicles, 2, spermiducts, 3, penis bulb, 4, penis, 5, penis sheath, or male antrum. The 

 slight development of the penis bulb, with its few muscles, in Trematods, is like what we 

 find in the Cestods, 3 but very unlike the enormous muscular sack of Planarians, again tes- 

 tifying to the close relationship existing between the two parasitic orders. 



The ovary (fig. 4, Ov.) is asymmetrically placed, and presents in transverse section a 

 nearly circular outline, its diameter being about the same as that of the larger testicle, 

 namely, two-thirds of the vertical diameter of the body. Like the testicles, it is sur- 

 rounded by a delicate membranous envelope, closely connected with the parenchym. The 

 ovary consists of numerous rounded cells, with a distinct membrane and large oval nuclei ; 

 part of the body of each cell is clear, the remainder is filled with a dark stained, finely 



1 Minot. Semper's Arbeit. I5d. in, lift. iv. 3 Cf. Leuckart. Parasiten, i, pp. 178, 263; and Sommer 



2 Moseley. On Stylochus, etc. Quart. Journ. Micros. Sci. und Landois. Bau der geschlechtsreifen Glieder von Botri- 

 Jan., 1877. ocephalus latus. Zeitsckr. wiss. Zool., xxn. (1872.) pp. 



54, 77. 



