DURING HIS SOJOURN IN THE WESTERN PACIFIC. 535 



From the way these ends project a section passing in the plane of the inner face of 

 ■ the wall of the organ cuts them, so that they appear to lie freely in the lumen of 

 the gland. This may account for many of the vesicles which help to fill the lumen 

 but I think not for all. Some of the vesicles have I think left the cells which 

 produced them and lie in the lumen of the gland. Outside the deeply stained basal 

 ends of these cells is another layer of large cells possibly destined to grow up into 

 the glandular inner cells, and still further outside is a well-developed stout layer of 

 longitudinal muscles. The muscle-fibres building up this layer are arranged in bundles, 

 and each fibre is tubular with a lightly stained contents and closely resembles the 

 fibres in the Leeches. They seem to be more specialized than any other muscle-fibres 

 in the animal. 



The vesicula seminalis opens by a small opening into the posterior extremity of 

 this organ, but I have not seen, in any of the six specimens I cut, any spermatozoa 

 inside the organ and indeed the anterior end of the vesicula is free from them. 

 In front this organ opens into a dome-shaped chamber. Between the two is stretched 

 a diaphragm and in the middle of this is a beautifully neat little funnel-shaped valve 

 with circular muscles in its walls (B, Fig. 4, Plate LIV. and Fig. A in text). 



I find it difficult to suggest any explanation of this organ, it may however 

 possibly be that its secretion is used to build up the spermatozoa into spermatophores. 

 If this be the case they must be extremely small as the lumen of the next part 

 of the male duct is very minute. Sedgwick' has suggested that in Trematodes, "It 

 may be that in some cases the penis is used, like that of Turbellaria, for hypodermic 

 injection of spermatozoa," and the organ of such hypodermic injection is replaced in 

 higher forms, i.e. Leeches and possibly Peripatus by spermatophores, but I am unaware 

 that these structures are known amongst Trematodes and even if they are the view 

 that they are formed by this enigmatical organ is highly conjectural. 



One feature is of interest and that is the mode by which the secretion leaves 

 the cell which elaborates it. Similar modes of secretion in which the secreta are 

 collected in a vacuole at the free end of an epithelial cell are well known in the 

 mammary gland, in the digestive glands of Crustacea, e.g. Astacus, and has been 

 described by myself in the nephridia — brown tubes — of the Gephyrea^ It is probably 

 more widely spread in the animal kingdom than is usually recognized. 



The dome-shaped chamber was as a rule empty but in one specimen it contained 

 a mass of minute granules in appearance resembling those of the vesicles but no 

 longer retained in vesicles. Scattered amongst these were a few spherical corpuscles 

 of unknown provenance, which stained very deeply. At its apex the dome-shaped 

 chamber opens by a small pore into the minute duct of the penis. This duct is at 

 first almost capillary and is contained in a muscular sheath with fibres running both 

 longitudinally and circularly. The tube has a cuticular lining and as it twists in the 

 substance of the penis and the penis is itself much coiled the lumen of the tube 

 appears many times in each section. After a course of some length this minute tube 

 widens, its walls cease to show the definite cuticular lining and they become relatively 



' .-1 Htudent's Text-Book of ZooUnjij. London, 1898. 



= Quart. J. Micr. Sci., Vol. xxxi. 1890, p. 1, and Vol. xxxii. 1891, p. 111. 



