THE ANATOMY OF A NEW SPECIES OF BATHYDORIS. 205 



oesophagus of Tritonia rises out of the dorsal surface of the bulb and well forward, the 

 main bulk of muscles being behind it. These and corresponding differences in the 

 muscular mechanism suffice to make good the statement made above, that the supposed 

 resemblances are confined to size and the presence of powerful jaws. It should be 

 mentioned that Bergh refers specially to Bornella in assigning Tritonid features to 

 Bathydoris ; without discussing the problematic relationship of Bornella to the 

 Tritonids, suffice it to state that the large buccal apparatus of that form differs from 

 that of both Tritonia and Bathydoris. 



It is indeed likely that these three cases of powerful and mandibulate mouth parts 

 are examples of convergence in unrelated types. The only other reference to a non- 

 Dorid affinity of Bathydoris is made by Eliot when he compares the armature of the 

 "stomach" with that found in Bornella. This comparison is strange, coming from an 

 author who has since, in the Ray Society's monograph, separated the two genera in 

 his first cleavage of the Nudibranchs. In any case the comparison is untenable, since 

 the two armatures are totally unlike in structure and position, that of Bornella being 

 situated in a region of the alimentary tube posterior to the point of entrance of the 

 liver ducts. On the foregoing grounds we must regard the proposed Tritonid and 

 Bornellid affinities of Bathydoris as inadmissible. It is, however, obvious that the 

 investigation of this last species has brought out certain features of the genus which 

 render necessary the reopening of the discussion of its affinities and, as we shall see 

 later, those of the Dorids generally. It is no less certain that the genus presents a 

 combination of characters far more significant than that considered by Bergh when he 

 assigned its affinities — namely, a Dorid gill of a primitive form, an asymmetrical heart 

 and efferent branchial system, blood glands placed far back on the course of the aorta, 

 a thin integument with scattered branchiate outgrowths, a diaulic reproductive system, 

 a liver distinct from the gonad and kidney, a brain with separate ganglia, a nerve 

 collar embracing the buccal bulb and not the oesophagus, and finally, but perhaps least 

 significant, a powerful buccal apparatus. 



That Bathydoris must be definitely placed among doridiform animals follows from 

 its possession of the following striking Dorid characteristics : — 



(a) The collocation of the anus, renal pore, and gills in the median line posteriorly. 



The gill is, however, more primitive than the typical rosette form common 

 among Dorids, though primitive gills are also found in such types as 

 Trevelyana and Nembrotha. 



(b) With the exception of the buccal mass and the protected oesophagus, the 



alimentary canal is Dorid, even to the possession of a gastric ceecum, and 

 those divergent features are adaptations to a coarser and more omnivorous 

 diet. The enlargement of the salivary glands is probably due to the same 

 cause. 



(c) The kidney is a Dorid structure, the reno-pericardial tube and syrinx being 



practically identical with those of Doris as described by Hancock 



