42 AUGUSTA ÄRNBÄCK-CHRISTIE-LINDE, NORTHERN AND ARCTIC 1NVERTEBRATES. 



Remarks. 



The genus Dendrodoa has been divided into two groups, the one comprises 

 species having an unbranched gonad, the other includes species having a branched 

 gonad. Only two species belong to the first-mentioned group, D. uniplicata Bonne- 

 vie and D. grossularia Van Beneden. D. uniplicata is a highly interesting form 

 which essentially differs from the other members of that genus. It is not represen- 

 ted in the collections of the Swedish Riksmuseum. 



As to the species D. carnea Agassiz which has been re-described by Van 

 Name (1912), it seems most probable that it is a form occurring within the range 

 of variation of D. grossularia. This supposition seems to be supported by the 

 author's own words, according to which specimens of D. grossularia »agree in prac- 

 tically all characters, external and internal, with the species last described (D. 

 carnea), but differ in having a much greater number of internal longitudinal vessels 

 in the branchial sac» (1. c. p. 588). From previous literature on the subject it 

 appears that the number of the internal longitudinal vessels is liable to variation; 

 it often depends on the age of the individual, on the occurrence as solitary or aggre- 

 gated form, or on other circumstances, why it is not to be considered as a valuable 

 character in distinguishing species from each other. 



Dendrodoa grossularia has long been known under the name of Styelopsis, a 

 name which has lately been changed (1912). It represents a well defined group. 

 Many authors are of opinion that it may be regarded. as a sub-genus and the name 

 Styelopsis retained for it. Between D. grossularia and the other Dendrodoae — D. 

 uniplicata excepted — there are, however, several points of agreement making the limita- 

 tions almost seeming. The features peculiar to the genus Dendrodoa and distin- 

 guishing it from the other Styelids are present also in D. grossularia. The gonad is 

 only one in number, placed on the right side, the oviduct is directed ventrally. — 

 Branched or unbranched gonad can hardly be regarded as a character of value. — 

 The male glands lie between the ovary and the body-wall; when well-developed they 

 form, in D. grossularia, irregular masses (Pl. 2, fig. 38). The väsa efferentia pass 

 around on the free side of the ovary and unite there, forming numerous short ducts 

 or openings (ef. Pl. 3, fig. 44). In other Styelids they usually form a vas deferens 

 running along the ovary and opening at the end of the gonad. 



Like many Dendrodoae the species grossularia is distinguished by the reduetion 

 of the folds and vessels of the branchial sac. In this respect it proves to be a 

 highly variable form. The individuals described as D. carnea (1. c.) having only 

 one fold on the right side and none on the left and resp. 4 and 7 vessels on each 

 side, seem to represent one extreme, specimens like those described by Selys-Long- 

 champs (1916 — 1917) represent the other: between them there are many interme- 

 diates. The last-mentioned author has observed that, in well-developed specimens of 

 the aggregated type, collected off Roscoff, 2 symmetrical, real folds, one on each 

 side, often occur; that on the right side is always more developed than that on 



