1911.] J. Stephenson: Some Aquatic Oligochaeta. 207 



to iv, its posterior limit coinciding with the second dissepiment 

 (») ; the crop occupies v — ^vi, the stomach vii — viii, but since 

 septa are not to be made out behind the oesophagus, these 

 limits are approximate only, and have been fixed by reference 

 to the setal bundles 



In longitudinal sections the pharynx is seen to be lined by 

 a thin layer of cuticle; its epithelium, like that of the oesophagus, 

 is approximately cubical. The cells lining the ' crop ' however are 

 very much larger, of irregular shape and varying height ; so that 

 the epitheliiun of this portion of the tract has an uneven out- 

 line, reminding the observer somewhat of the inner layer of Hydra, 

 and suggesting the possibility of intracellular digestion. Chlora- 

 gogen cells are scanty or absent on the crop, abundant on the 

 stomach. 



The circulatory system could not be made out. 



Annandale has noted the presence of an otocyst in the 

 brain in this species, — a relatively large, globular, transparent 

 cyst. I have not found any trace of such a cyst in the preserved 

 specimens which I have examined, either mounted whole, or 

 in longitudinal sections : the brain is large, and consists of two 

 parts, an outer cellular surrounding a spherical granular looking 

 mass. There are however a number of enigmatical appearances 

 in connection with the brain of various species of Chaetogastcr ; 

 thus, besides that which led in the present case to the suspicion 

 of an otocyst, there is the structure described by Vejdovsky 

 {System und Morphologie der Oligochaeten, p. 38) in C. diastrophus 

 C in dem Binschnitte zwischen den Gehirnlappen befindet sich 

 eine glanzende, scharf contourirte braune Chitinplatte ") and 

 figured in his pi. vi, fig. 12 ; there is the densely pigmented 

 body, possibly functioning as an eye, described by Annandale 

 {Journ. As. Soc. Bengal (N. S.), vol. ii, No. 5, p. 189) in a species 

 not named, as well as the sense-organ in the brain of C. bengalensis 

 (Annandale, ibid., vol. i. No. 4, p. 117) ; there is the bright, refractile 

 body, in the same situation as the brown chitinous plate of 

 C. diastrophus, described by me in C. punjabensis [Rec. Ind. Mus., 

 vol. i, pt. 2 ; and cf. pi. v, fig. 7) ; and the opaque granular mass, 

 again in a similar situation, in C. orientalis (= C. pellucidus, Rec. 

 Ind. Mus., vol. i, pt. 3; and cf. text-figs. 4, 5). 



The anterior part of the ventral nerve cord is, in a number 

 of species of the genus, covered by nerve cells which have no 

 segmental arrangement. In the present species the cord is 

 interesting as showing a fairly distinct aggregation of the nerve 

 cells into separate gangha. There are no intervals, in the anterior 

 part, where the cord is bare of cells ; the cells invest the whole 

 length of the cord as far back as the second setal bundle (segment 

 vi), so that their aggregation into ganglia, though distinctly 

 indicated, is still incomplete. There are two such aggregations in 

 the pharyngeal region, the first of the two being at the level 

 of the first setal bundle (segment ii) ; and three behind the 

 pharynx, the last of these being opposite the second setal bundle 



