136 J. Stephenson: Description of an OligochcBte Worm. [VOL. I, 



The body-cavity is extensive, and (with the exception already 

 noted) was not seen to contain corpuscles. The septa are delicate 

 partitions showing swellings indicative of nuclei [v. fig. 7). 



Circulatory system (fig. 8) — The dorsal vessel extends from 

 the hinder end of the body to the prostomium, and is pulsatile 

 along its whole length except for a very short distance in front, 

 anterior, that is, to the level of the refractile particle of the cerebral 

 ganglion {v. inf.) close to which it runs ; the contractions proceed 

 from behind forwards. There are two lateral vessels, of calibre 

 approximately equal to that of the dorsal vessel, which encircle the 

 oesophagus, uniting ventrally with the ventral vessel ; they are also 

 contractile, the contractions progressing from above downwards. 

 The ventral vessel cannot be traced quite as far forward as the 

 dorsal ; it is of about the same calibre, and is nowhere pulsatile. 

 There appears to be a fine plexus of capillaries on the external 

 surface of the crop and stomach {v. fig. 9). The blood is colour- 

 less and contains no corpuscles. 



The Nephridia aie much-coiled fine tubes, which, however, be- 

 come thicker, with more granular walls , near their external opening ; 

 this is situated a short distance in front of the bundle of setse of the 

 same segment. The canal is somewhat dilated just before it opens 

 to the exterior. I could not distmguish the beginning of the tube ; 

 no ciliary action was visible in any part of it ; nor did the nephridia 

 appear to be connected with the septum in front of them. Nephridia 

 are constantly found in the seventh and eighth segments at the 

 sides of the stomach ; for the rest, their distribution varies {v. fig. 

 10 a and b). They are not found in any of the segments that have 

 recently formed. 



Nervous system. — The cerebral ganglion is situated far for- 

 wards, just behind the prostomium, occupying a space correspond- 

 ing to the buccal cavity and anterior part of the pharynx. It is 

 not distinctly bifid, but rather irregularly lobulated in shape {v. fig. 

 7). One particular portion, spherical in shape, slightly more re- 

 fractile than the rest, and situated at the level of the junction of 

 buccal cavity and pharynx, stands out in all specimens ; posteriorly 

 there is closely opposed to it a bright, somewhat granular mass, 

 semilunar in shape as seen sideways {v fig. 7). I am unacquainted 

 with a similar structure in other forms, and have no suggestions to 

 make as to its function, unless it be a degenerate otocyst. 



The circumbuccal commissures are situated at the level where 

 the buccal cavity passes into the pharynx. The subpharyngeal 

 ganglionic mass is irregularly lobulated, broad from side to side, 

 narrowing posteriorly to become the ventral nerve-cord. Some 

 small lobes frequently appear entirely detached from the main 

 nerve-mass. The ganglia of the ventral cord are placed at the level 

 of the setae in each segment ; in the achsetous interval (3-5 segm.) 

 there are irregular swellings on the cord, which do not appear to have ' 

 the definiteness of the ganglia in the following segments. The ventral 

 cord is of considerable thickness and is always very easily seen ; it is 

 not united with the epidermis. Its double origin is perhaps indicated 



