ON ÜIPLOZOON NIPPOXICUM, N. SP. 155 



otlier, but that one is always a little either to the left or to the rio-ht 

 side of the other, according as the worms are united by the corres- 

 pondiiiiT sides of their bodies. This feature is usually less noticeable 

 in the anterior hah es, l)ut it can easily he brought to view by bring- 

 ing them close to each other. It is caused, no doubt, by the flict 

 that the bodies of the two individuals are closely united onkj at the 

 point of crossing ; as may be seen, if one phices two pie(^es of straw 

 against each other in the form of a «-ross, and presses l^heni together 

 between two hngers at the point of rrossing. Beside this imperfect 

 apposition of the corresponding halves ()f the two individuals, must 

 also be noticed the twist, to which each is subjected at the place of 

 crossing, in consequence of the fict that one grasps with its ventral 

 sucker the dorsal papilla of the other. To this twist, though very 

 small in degree owing to the presence of the notch already men- 

 tioned, must be attributed the common occurrence that, when the 

 ^vorni is killed under the pressure of a cover-glass, tlie anterior and 

 posterior halves (jf tlie same individual present to view opposite sides 

 of the b()dy — the anterior half presenting the dorsal if the other half 

 presents the ventral side, and vice versa. I'he two individuals are 

 united with each other by their sides, so that here a deep indentation 

 arises — the notch already spoken of. Here the epidermis is absent, 

 and the muscular layers of the two individuals are directly applied 

 to each other. Zeller describes a direct connection between the vas 

 deferens and " Laurer's canal" of the two individuals ; but a careful ex- 

 amination has ctuivinced me that this view is erroneous. I lind Laurer's 

 canal to open distinctly into the intestine, and the vas deferens of one in- 

 di\ idual into the yolk-duct of the other, as will be {)roved later on. In 

 this connection, it may be mentioned that the same writer thinks the 

 Diporpa incapable of "eine noch weiter gehende Entwicklung ohne dass 

 zuvor die Copulation mit einer zweiten Diporpa zu Stande gekommen 



