26 W. "nALDWIN SPENCER. 



portions of the reproductive organs. In the male it lies at the 

 anterior end, completely dorsal to the reproductive organs ; but 

 further back, in the region of the testis, it lies below the level 

 of this. Thevesiculse seminales, which arise from the anterior 

 end of the testis, pass through the middle of the gland — a feature 

 which, again, is more noticeable in young forms (figs. 6, 17, 18). 

 In mature forms the vesiculse are so large in comparison to the 

 glands that the latter appear to be compressed between them 

 and the alimentary canal, and thus the genital ducts have the 

 appearance of passing between the body-wall and the gland, 

 as they are described as doing in the adults of other species 

 (fig. 17). Careful examination, however, reveals the fact that 

 little masses of cells are present, the remnants of the part of 

 the gland lying external to the vesiculse. Fig. 17, which is a 

 camera drawing representing a transverse section of a young 

 male, will serve to show clearly the relation of the structures 

 at that stage. 



In the female (fig. 7) the gland occupies a similar position 

 by the side of the alimentary canal lying beneath the median 

 ovary, though the latter and the glands are both pressed up 

 against the dorsal wall by the swollen and coiled uterus in the 

 adult form. As in the male, so in the female, the ducts leading 

 off from the anterior extremity of the gonad pass on each side 

 right through the centre of the gland (fig. 22, Od.). 



In P. proboscideum Stiles and Lohrmann have described 

 the gland as being composed of two different kinds of cells — a 

 larger and a smaller. Stiles^ figures the smaller ones as lying 

 close to the duct in the centre, and as being surrounded by a 

 layer of much larger cells. 



In the form now being described there is no such distinction 

 into two kinds of cells ; some, indeed, are smaller than others, 

 but all, as is not the case in P. proboscideum, take stain 

 (borax carmine) in the same way, and there is every gradation 

 in size between the largest and the smallest. They vary in 

 size from '25 mm. to '08 mm., the largest cells being always 

 those found in the parietal glands, though, so far as their 

 ' Loc. cit., p. 128, Taf. viii, flg 47. 



