THE ANATOMY OP ONCHOLAIMUS VULGARIS, BAST. 123 



marked chromatin granules, and one or two pseudo-nucleoli. 

 On passing further from the fundus, the nuclei increase in 

 size, the protoplasm becomes relatively less, then cell outlines 

 appear; the nuclei have increased to •00645-"00753 mm., and 

 the chromatin takes the form of a network (PL 7, fig. 17, 

 sg.). About the commencement of the last quarter of the 

 region the sperm mother-cells begin to divide, the chromatin 

 is aggregated in larger granules, the nuclear membrane dis- 

 appears ; still further on the chromatin takes on a star-shape. 

 The cells (mature spermatozoa) ai-e here more numerous and 

 smaller, '0043 ram. in diameter, are not so closely packed, 

 and are surrounded by some residual protoplasm. Spermato- 

 zoa are found in the anterior portion of the ductus. The rest 

 of this organ is generally found to be empty. 



The ductus ejaculatorius is a straight cylindrical tube, 

 although at its commencement slightly flattened. The pos- 

 terior testicular region opens into it a short distance behind 

 its origin from the anterior. 



Its wall consists of two layers — internal epithelial, external 

 muscular (PI. 7, fig. 17, db.). The epithelium is cubical, 

 becoming columnar towards the termination of the tube. The 

 cells are highly vacuolated, and the free surfaces pi'esent a 

 frayed-out appearance, as if a secretion had been discharged. 

 In places this secretion can be made out as numerous acido- 

 phil granules. 



The muscular wall consists at first only of a layer of circular 

 fibres. Flattened nuclei with a fine film of protoplasm can 

 be made out on the outer surface, no doubt the nuclei of this 

 layer. In the posterior quarter there is also an external layer 

 of longitudinal fibres. 



At its termination the ductus unites with the rectum to 

 form the cloaca (text-fig. 1, cL). As this latter structure is 

 intimately connected with the copulatoiy apparatus, I shall 

 describe it here rather than under " The Alimentary System." 



It is a short chamber, at its commencement roughly 

 cylindrical in section, but becoming flattened towards its 

 external opening, which is slit-like. 



