39 



nucleus is situated („glandes finement granulées" de Cerfontaine). More 

 over the clitellum appears also to contain unchanged hypodermis-cells, 

 the nuclei of which lie in a continuous row, quite near the surface 

 (PI. II. fig. 17). The glandular thickening of the clitellum usually com- 

 mences with the XVIIIth segment, but on transverse sections the 

 first glandular cells are already visible in the XHIth segment; there- 

 fore the clitellum appears to extend itself much more forward, as 

 also visible externally in some specimens. The glandular layer has 

 nearly the same thickness over the whole periphery of the clitellum, 

 but the distribution of its glandular elements is not the same every 

 where (pi. II. fig. 18). At the dorsal side there is a couple of peripherical 

 layers of coarsely granular, tubular cells, followed interiorly by six 

 to eight layers of finely granular clubshaped cells; at the ventral 

 side the same arrangement is to be seen only in its median portion, 

 between the ventral bristles. The lateral portion of the ventral side 

 only consists of coarsely granular cells. 



A similar arrangement is stated by Ceepontaine to exist in the 

 clitellum of Lumbricus terrestris; in this species he found also in the 

 tubercula pubertatis modified club-shaped cells, containing a more 

 coarsely granular substance. 



The diagram (fig. 18) shows that the muscular layer does not enter 

 into the substance of the ridge; its internal substance consists of a 

 network of fine connective fibres and ramified cells. Several blood- 

 vessels are also to be found therein. 



External openings of the genital organs or of the nephridia are not 

 visible; dorsal pores are absent. 



In the vicinity of the clitellum curious oval grooves, with a dark 

 protuberance in their centre, are visible (pubertätsgrübchen 

 Michaelsen). Neither the arrangement nor the number of these pu- 

 berty-grooves is constant. In the XXIIth segment they are usually to 

 be found on each side in the series of the external ventral bristles, 

 in segment XXIII, XIX and XX however in the series of the infe- 

 rior dorsal bristles; they can also be met with in segment XXXII 

 and XXXIV. These grooves often are situated assymetrically f. i. at the 

 left side of the body in segment XVIII and XIX , at the right side in 

 segment XIX and XX. In transverse sections (fig. 17) they appear to 

 be cup-shaped organs, which are very obvious by their vitreous ap- 

 pearance and lie totally embedded in the glandular layer of the clitel- 



