26 



CTENOPHORA. 



point are correct, and thus the peripheral canal system has the same origin in both Tjalfiella and 

 Ctenoplana assuming that the "endlobes" of Willey are those between the two outer pairs of costse 

 in his Fig. i. In the very diagrammatical figure n of Willey's paper these lobes would sooner be 

 taken to represent the tentacle vessels, as what Willey later on mentions as the "terminal lobes" 

 decidedly represent the tentacle vessels. It seems that Willey has not reached full clearness on this 

 point; but I cannot doubt that the branching canals really arise from the outer lobes, not from the 

 tentacle vessels. 



Fig. 3. Vertical section, somewhat oblique, in the transversal plane, through Ctenoplana Kowakvskii. (After Korotneff. Op. cit. 



Taf.VIII. Fig. 3). The letters are those of Korotneff. Lm. "grosse Langsmuskeln" (= tentacle); M. Mund; Mg. Magen (= folds 



of the pharyngeal cavity); nik. "Magenkanal 1 ' ( probably sections of the tentacle); Rp. Rippenplatten ; st. "Sinnestentakeln"; 



T. grosse Tentakeln; tm. dorsoventrale Muskeln; tr. Trichter (infundibulum). 



Regarding the histological structure of the peripheral canal system I venture to suggest that 

 there will prove to be perfect accordance between the two forms. It is true, Korotneff states them 

 to be lined all round with a simple, uniform epithelium (comp. his fig. 9) and Willey (Op. cit p. 328) 

 even states that they appear in sections "merely as the spaces partitioned off by the dorsoventral 

 trabeculse, which Korotneff describes as dorsoventral muscles". But in the figure 4, copied from 

 Willey (Op. cit. PI. 21, Fig. 5), a rather distinct indication of the two walls of high epithelium is 

 seen in the space directly below the genital organ, as described above for Tjalfiella. I do not doubt 

 therefore that the histological structure of this canal system will prove to be identical with that of 

 Tjalfiella, so that the peripheral canal system, upon the whole, is evidently another essential point of 

 resemblance between Ctenoplana and Tjalfiella. 



The central part of the gastrovascular system, however, appears to differ very considerably 

 in the two genera, both in its general configuration and in its anatomical and histological structure. 

 A very conspicuous feature is the possession of a pair of large lobes in the sagittal plane. This 

 is a feature entirely unknown in typical Ctenophores; but in Coeloplana a corresponding pair of 

 lobes occur, from which a system of branching canals arise; it might then perhaps not seem un- 

 reasonable to suggest that also in Ctenoplana they give rise to branching canals. In Tjalfiella there 

 is no trace of such sagittal lobes from the gastrovascular system, probably as a consequence of the 

 compression of the body in the sagittal plane, while in the flattened, widened body of Ctenoplana and 

 Coeloplana there is room enough for this structure. This is the first difference of any importance 



