708 



THE ANATOMY OF BOTHRIOCEPHALUS LATUS. 



their form, usually ovoid, and somewhat produced inwards. The 

 external portion protruding between the subcuticular cells is thus 

 often drawn out into a conical point, which at the first glance 

 suggests the presence of an opening, which has been maintained by 

 some observers. Contrary to appearance, however, the expulsion of 

 the contents takes place at the end turned inwards, and that by 

 means of a duct, which is indeed only recognisable when it contains 

 yolk, which is by no means always the case. At first narrow and 

 inconspicuous, perhaps even without a distinct wall, these ducts 

 gradually unite to form canals, which extend between the yolk- 

 vesicles and the longitudinal muscular sheath, and finally develop 

 into a system of tubes, often conspicuous (even under a low power) 

 on the ventral surface, because of their contained yolk and wide 



K 



FIG. 370. Segment of BotJiriocepkalus with yolk chambers and "yellow ducts," 

 after Eschricht. ( x about 8.) 



extent. Eschricht even recognised this efferent apparatus, and 

 connected it with the "granular heaps," although he, under the 

 influence of Ehrenberg's polygastric view of the Infusoria then in 

 vogue, was at first inclined to regard the latter as stomachic sacs. The 

 " yellow ducts," whose discovery so excited Eschricht that he could 

 hardly wait for the daylight in his anxiety to see them again, are 

 nothing more than the branches of this efferent apparatus, which 

 radiate outwards from the region of the so-called " knot," through the 

 median area, to the lateral portions of the ventral surface. They 

 exhibit sometimes a straighter, sometimes a more coiled course, are 

 at intervals often sinuously enlarged, and exhibit, besides, consider- 

 able variety in their degree of repletion. The walls are thin without 

 any histological differentiation, except that in the larger branches a 

 distinct membrane can be recognised. 



It is a striking fact, as Eschricht rightly pointed out, that the dis- 



