544 



attached ends of which are external circlets of cilia. In the anterior 

 segments they are almost colourless ; behind their walls are of a bright 

 golden yellow owing to their containing numerous yellow »hepatic« 

 cells. 



Ehlers's drawing [1. c. Taf.lV, Fig. 3] of the supposed segmen- 

 tal organ is in fact a very faithful representation of one of these caeca 

 as seen in Polyno'é perclara, mihi, save that the internal orifice is re- 

 presented as opening into the body-cavity instead of into the intestine, 

 and the bands of muscular fibres connecting the caecum with the walls 

 of the parapodium in the neighbourhood of the rosettes of cilia are re- 

 presented as canals leading from the cavity of the caecum to the 

 exterior. 



The true position of the segmental organs of Polyno'é is very 

 different from this. On the ventral surface of the body close to the 

 base of each parapodium is a smooth elevation the integument of which 

 is very richly provided with vermiculate and flask-shaped subcuticular 

 glands. At the posterior and external angle of this elevation is a 

 minute projecting process — the ventral tubercle^. It is of vary- 

 ing shape; in some species short and vase-like with longitudinally 

 folded walls; in the species in which I have studied it more specially 

 [Lepidonotus oculatus Baird, Polynot perclara and P. mytilicola, mihi) 

 it is a longer or shorter, cylindrical, cirriform process. It is traversed 

 by a central canal with dilatable, ciliated walls, which opens at its 

 extremity either by a rosette of several mouths or by a single orifice — 

 the external opening of the segmental organ. The canal is continued 

 from the base of the process inw^ards and slightly forwards and ends in 

 the body cavity at some distance from the middle ventral line. The 

 walls of the inner portion of the canal are glandular and contain red- 

 dish-yellow bodies, some of which may on the application of slight 

 pressure be seen to pass out through the external aperture; like the 

 outer portion of the canal it is lined with cilia. Of the form of the 

 internal extremity of this canal I have not succeeded in satisfying my- 

 self, but there is no doubt that it opens into the perivisceral cavity. I 

 found in several specimens spermatozoa in the act of being discharged 

 tlirough this canal. They were driven along by the action of the cilia 

 into the external portion of the canal, which they distended somewhat 

 in some instances by their accumulation, and were gradually emitted 

 by the external aperture or apertures. In the female the tubercle is 

 usually shorter than in the male and the aperture wider and never 



5 The only attempt I can find to explain the nature of this ventral tubercle con- 

 sists of a conjecture by Prof. Huxley Anat. of Invertebrates p. 231) that it may 

 possibly be connected with tlie reproductive function. 



