T, B. ROSSETER ON THE ANATOMY OF DICRANOTJiNIA COROXULA. 363 



external, and does not deal with the internal topograi^hical 

 anatomy of this helminth. 



Male Organs. 



The genital cloaca with its genital pores is unilateral and 

 dextral. It is an elongated cavity. It is situated on the extreme- 

 margin of the proglottis, at the anterior apical end, and is 

 partially overlapped by the preceding segment. Its shape 

 is dependent in a great measure on the muscular contractility 

 and expansion of the strobila ; and its contour, together with the 

 cavity, is not obliterated in the uterine segment. Its long diameter 

 is O'OT mm., and its cross diameter 0*023 ; its depth to the male 

 orifice is 0*04 mm., and to the female 0*047 mm. 



The male genital apparatus consists of the cirrus and cirrus- 

 pouch, the vesicula seminalis, and the testicular organ with its 

 vas-deferens (Fig. 5 a). 



The male genital tract is situated in the anterior portion of 

 the proglottis ; it occupies two-thirds of the whole length of it, 

 and runs somewhat dorsally and ventrally. 



The testis is not, as in Tcenia clepressa^ scattered over the 

 interior of the proglottis, or tri-form as in Drep. venusta and 

 D. anatina ; but it is a large monoecious epithelial sac, situated 

 dorsally in the anterior distal third of the segment, and at its 

 proximal end contracts itself into a tortuous efierent canal 

 (Fig. 5 a, a — h). The spermatozoa are secreted in follicles, which 

 are spread over the epithelial wall of the testicular sac. The- 

 sperm atospores, which are budded off, are oval nucleated cells, 

 and are aggregated together in colonies forming spermatosphere& 

 (Fig. 6). They do not increase their individuality by division of 

 the whole cell, as in the spermatospore of the earth-worm ; but 

 the central nucleus splits up into minor (reticulated) cells, and 

 the individual spermatozoon is evolved from these daughter 

 cells. Thus a single spermatoblast produces a number of 

 spermatozoa. When seen in the examining media, the spermato- 

 blasts bear a striking resemblance to the floating fronds of 

 Lemna polyrhiza. The spermatozoa from each spermatoblast form 

 themselves into one common strand, and these strands coil or 

 entwine round each other in the form of a " hempen warp." 

 The tails of the spermatozoa are always free, and they are 

 spread out like a number of loose threads (Fig. 7). In this 



