352 MR. A. G. BOURNE ON CERTAIN POINTS 



ence even of these ventral papilla? has heen so very generally overlooked. While 

 Claparede, Mahngren, and Ehlers insert it occasionally in their figures, the only 

 references to it are made by Huxley and Grube. Claparede, however, does describe the 

 papiike in Ilermadion fragile, and suggests that it may be the orifice of the segmental 

 organ. Huxley *, in his account of the anatomy of P. squamata, which was based upon 

 his own observations, says : — " Springing from the neural surface of the somite, close to 

 the parapodium, there is a small pyriform tubercle, divided by longitudinal grooves into 

 about eight segments. This is possibly connected with the reproductive functions." 



Grube f recognizes its wide-spread existence : — " At the point where the parapodium 

 springs from the ventral wall of the body, exists in all Polynoina a very small papilla 

 (ventral papilla), which, at any rate in pregnant examples, is perforated, and serves for 

 the passage of the eggs to the exterior. The animals in which they run out to a point 

 are probably males. I have repeatedly found sticking to the spots slimy masses, which, 

 on account of their resemblance to those observed in living Heteronercis forms, I take 

 to be spermatozoa. This papilla is generally present, but, as a rule, absent upon the first 

 3-0 seta-bearing segments." 



I have had an opportunity of examining a very large number of living Polynoina, 

 representing some sixteen or seventeen different species, and am in a position to corrobo- 

 rate Grube's statement as to its universal existence. Both Huxley and Grube accurately 

 describe its position ; it springs from the ventral wall of the body itself, and not from the 

 parapodium. It varies very much in size in different species: in P. clava it is large 

 and thick (PI. XXXVI. figs. 17 & 18) ; in P. squamata it is mucli longer and thinner 

 (fig. 19) ; in P. spinifera, Ehl., it is very slightly developed (fig. 20) ; and in P. areolata, 

 Grube (fig. 21), it is merely a slight swelling of the body-wall, which is perforated. In 

 all the other species examined the extent to which it is developed is intermediate to 

 these conditions. 



As Huxley points out, it may exhibit eight longitudinal grooves upon its surface. At 

 the breeding-season the body-cavity is filled with the generative products, rendering the 

 body-wall perfectly tense, and they are forced into the space in the wall of the papilla ; 

 the grooves then disappear. The constancy of their number points to some structural 

 basis ; but their absence in such a large number of species indicates that they have no very 

 great significance. 



The papilla} are absent, as a rule, from the eight most anterior somites, and are con- 

 tinued down to the penultimate somite. In P. clava there are eighteen pairs. 



Careful and continued examination of various species has proved that they are not 

 connected with the reproductive functions, but are the apertures of the nephridia or 

 segmental organs, as Claparede surmised in his Hermadioti fragile ; serial sections 

 combined with examination in the fresh state, both in the compressorium and after 

 teazing, have revealed the whole structure of these organs (PI. XXXVI. figs. 22-25). 



* Huxley, ' The Anatomy of the Invertebrated Animals,' p. 231. 



f Grube, " Bemerkungen iiber die Familie der Aphroditeen, III. Polynoina," Bericht der schlesischcn Gcsellschaft, 

 187G, pp. 2G-52. 



