ON TEMNOOEPHALA. 295 



The tentacles are also to be regarded as sense organs as 

 well as aiding in locomotion and prehension. There is nothing, 

 however, in the structure of these organs, except the presence 

 of large nerves, specially connected with their sensory func- 

 tions; the epidermis and the muscular layers resemble those 

 of other parts of the body. 



Reproductive Organs. 



The common genital aperture (PL XX, fig. 5 } g.) is a tolerably 

 large slit-like opening situated a little distance in front of 

 the sucker. It is surrounded by a special set of muscular 

 fibres which serve the purp.ose of a sort of sphincter. It 

 leads into a common genital cloaca, into which on one side 

 projects the penis, while on the other is situated the female 

 opening. This cavity is lined by a continuation of the cuticle 

 and epidermis of the outer surface, the cells of the latter being, 

 however, considerably elongated, forming an almost columnar 

 epithelium, external to which is a thick layer of muscle. 



The testes(7e.in PI. XX,fig.6; Pl.XXI,fig. 4; and PI. XXII, 

 fig. 17) are two pairs of large glands of cylindrical form, with 

 the long axis longitudinal, lying at the sides of the alimentary 

 canal, and extending throughout the length of the body from 

 the pharyngeal region to some distance behind the sexual 

 aperture. The two testes of the same side are connected by a 

 slender duct. They are invested with an extremely delicate 

 layer of muscle, which is continued into the wall of the duct 

 and of the vas deferens. Though there are only two pairs 

 of testes, these partake to some extent of the segmented 

 character of the animal — being partially subdivided at the 

 sides by a deep transverse incision opposite each of the mus- 

 cular partitions through which, however, the main substance 

 of the gland is continued uninterrupted. The spermatozoa 

 have pear-shaped heads, about '0046 mm. in diameter, and 

 slender fiagella, '083 mm. in length. 



The two vasa deferentia are slender tubes, which, passing 

 inwards from the posterior testes towards the middle line of 

 the body, meet to form a large seminal vesicle or spermatic 



