200 bulletin: museum of comparative zoology. 



or invalidating this homology. I hope soon to undertake such a 

 study. 



Kingsley ('89, p. 32, foot-note) has suggested that the genital outlets 

 represent part of a metamerically repeated series of ducts. The female 

 and male genital openings in Decapods, for example, occupy the bases 

 of the eleventh and thirteenth pairs of appendages respectively ; their 

 similar position is, in Kingsley's opinion, "inexplicable upon any other 

 ground than that the oviducts and vasa deferentia are themselves modi- 

 fications of pre-existing metameric organs, and the only organs in the 

 Annelids which would answer the requirements of the case are the 

 nephridia." 



The first part of his proposition is strengthened by evidence given by 

 Bateson ('94, pp. 152-155), who found that in over three per cent of 

 the females of Astacus fluviatilis examined, there appeared supernumer- 

 ary oviducal openings. These were either bilaterally symmetrical, or 

 on one side only, and were not necessarily situated in the segment 

 adjacent to the normal opening, but were sometimes removed to the 

 thirteenth segment. Dissection showed that, in cases where such su- 

 pernumerary openings appeared, the oviduct was branched and com- 

 municated with all the openings, which were presumably functional. 

 Oviducal openings, were found on the eleventh (normal), twelfth, and 

 thirteenth segments, but no such repetition of genital openings was 

 noted in males. It is probable, then, that Kingsley's proposition that 

 the genital ducts are members of a metameric series is valid ; but 

 whether or not they are homologous with the nephridia of Annelids is 

 quite another question. There are in Annelids other metameric organs 

 of somewhat similar position, of which these ducts in Crustacea might 

 be representatives, e. g. the setigerous glands or the dorsal pores. The 

 fact that in Annelids the genital products are in many cases carried to 

 the exterior by the nephridia, or by modified nephridial ducts, lends 

 support to Kingsley's contention ; but we cannot rely solely upon the 

 evidence of analogy from which to draw conclusions as to homology. 



The evidence on the ontogeny of the genital ducts and their open- 

 ings in Crustacea is not very complete, but in the main it points to 

 their peripheral portions at least as being ectodermic invaginations 

 entirely distinct from the primary reproductive organs. If this be 

 confirmed, it will add support to the view that they are homologous 

 with the ectodermic portion of the nephridium of Annelids ; but it 

 must be remembered that the setigerous glands of Annelids also have 

 a similar origin. 



