176 WHEELER. [Vou. IX. 
rami separate, that of the right side being considerably longer 
than that of the left. I conjecture that in the fusion, which 
must take place very soon after hatching, the tip of the 
shorter ramus unites with its fellow in such a way that 
the whole tip of the primitively longer ramus is left as the 
unpaired stem of the adult. 
The fused condition of the posterior rami of Syucelidium 
was described and figured by Ryder (822, Fig. 10). v. Graff says 
of B. candida: “Die beiden hinteren Darmschenkel sind in 
der Jugend getrennt, bei erwachsenen Thieren aber (immer ?) 
durch eine Queranastomose verbunden.” This condition I 
have also noticed in three adult specimens of B. candida, but 
the fusion is of a very different nature from that obtaining in 
Syncelidium. In the former species the posterior rami are 
of equal length and extend into the tail. In the cases 
which I have examined, the fusion occurs between two mesial 
diverticula, thus forming a connection between the rami, like 
the horizontal bar which joins the two upright pieces in the 
letter H. This vinculum does not occur in the young or half- 
grown specimens of b. candida. In Bb. propinqua I have seen 
no trace of it. 
Only one other Triclad is known to me which exhibits a 
union of the posterior rami—a species of Dendrocelum 
(D. nausicae) from Corfu and Cephalonia, long since described 
by Oscar Schmidt (61). His Fig. 1, Pl. Il, shows that the 
union is brought about by a confluence of a pair of mesial 
diverticula, and not by a fusion of the rami themselves. The 
species is interesting as presenting a condition intermediate 
between Syuceliditum and Bdelloura, for one of the posterior 
rami is distinctly shorter than the other.? 
Histologically, the gut of Syxcelidium does not differ from 
that of other Triclads as described by Lang, [jima, and 
Chichkoff. 
1 In Boas’ Text-book of Zoology (’90, p. 150), there is a figure of Dendrocelum 
lacteum attributed to Oscar Schmidt, and showing several anastomoses between 
the posterior gut-rami. In N. American specimens which I regard as belonging 
to this species I can detect no such conditions, the two posterior rami being quite 
separate. 
