IN THE ANATOMY OF THE POLYNOINA. 353 



Ehlcrs * has described a segmental organ in P. pellucida as a contractile sac lying in 

 the parapodium and opening externally by several (4-6) ciliated mouths upon both its 

 notopodial and neuropodial faces, the internal opening lying near the dorsal wall of the 

 somite. Ehlers describes these as occurring in every somite from the second onwards. 



Claparede t states that he has observed the ciliated rosettes of Ehlers in P. lunulata, 

 but, in spite of the transparency of the animal, has been unable to acquire the conviction 

 of their communication with the segmental organs. I have not studied P. pellucida, 

 but, from the analogy of other forms, strongly suspect that what Ehlers has seen is not 

 the segmental organ at all$. The nephridium, in all the forms which I have examined, is a 

 funnel-shaped tube, the walls of which may be much plaited and folded, but it does not 

 appear to be at all convoluted. This tube opens internally in the ventral region of the 

 body, close to the two ventral muscular masses, and then runs posteriorly ventrally out- 

 wards. Near the base of the papilla its lumen dilates, forming a small vesicle, whence a 

 straight tube of even diameter traverses the axis of the papilla. There is no muscular 

 development in connexion with it at any part of its course ; it never enters the para- 

 podial region at all ; and although ciliated along its whole length from the internal 

 funnel to the vesicle, no cilia are developed at its external opening. 



Fig. 22 is a diagrammatic drawing compiled from the series of sections &c. 



Fig. 23 is a transverse section of the papilla, and shows the longitudinal grooves, the 

 epidermis, which is continuous with the epidermis of the rest of the body, and the ciliated 

 epithelium cells lining the excretory tube ; between these is a layer of connective tissue' 

 branched corpuscles in a connective jelly. 



Fig. 24 represents a section of the tube near the internal opening, while fig. 25 is an 

 intermediate section in the region of the vesicle. The body-cavity is packed with ova, 

 which press the two walls of the vesicle together, and in many cases almost occlude the 

 lumen. The ova force their way in between the nephridial epithelium and the epidermis, 

 and thus, on an external examination, give the impression of being within the lumen 

 of the papilla ; and this appearance it is which has led previous observers to connect these 

 papilla? with the reproductive function. 



How do the generative products pass to the exterior ? There certainly are no special 

 ducts ; and they cannot either find exit through those nephridia or by pores, temporary 

 (i.e. ruptures) or permanent, in the body-wall. Ehlers and Sars both mention such 

 pores as existing in the parapodial wall. The generative products are known to escape 

 by rupture in other marine Annelids, e. g. Polygordms. All my observations upon living 

 animals favoured this view. I never actually saw the ova or spermatozoa spontaneously 

 shed ; but the slightest irritation when the body-wall was tense caused a slight rupture here 



* Ehlers, ' Dio Borstenwurmer,' 1864-1863, p. 116. 



t Claparede, ' Annelides Chetopodes du Golfe de Naples,' p. 374. 



X Since this was written, Mr. "W. A. Haswell, M.A., B.Sc, in " A Monograph of the Australian Aphroditea " (Proe. 

 Linn. Soc. New South Wales, vol. vii.), has described the segmental organ in P. (Antinoe) prceelara and P. (Antinoe) 

 Wdhlii allied to P. pellucida, Ehlers. That author has also arrived at the conclusion that Ehlers has not seen the 

 true segmental organs, but only intestinal cteea ; he describes the former as opening at tho ventral tubercles, but does 

 not give any figures. 



