No. 2.] ANATOAfV OF BDELLODRILUS ILLUMINATUS. 503 



epithelium extends as deeply staining nucleated processes of 

 protoplasm, which often lose their distinct cellular boundaries. 

 The epithelium is largely displaced ; and sections often show a 

 predominance of muscular over epithelial elements in this layer. 



Glands are very richly developed in connection with the epi- 

 dermis of B. illuminatus ; and while all are constructed of 

 similar elements, they differ much in the size and arrangement 

 of these elements. The elements are unicellular glands some- 

 what of the goblet cell type. In most cases they consist of an 

 enlarged irregularly polyhedral body containing the nucleus, 

 and tapering at one end into a slender, more or less elongated, 

 ductule. The only exceptions are those glands which are 

 referred to as salivary and bursal glands. 



Certain small mucous glands are very generally distributed 

 over the skin ; especially on the head, where they are regularly 

 arranged in several transverse rows. They may be unicellular, 

 or consist of three or four unicellular glands, the ductules of 

 which are twisted or spiral. 



On the sixth and seventh somites such glands become 

 greatly increased in number and size ; the body walls, particu- 

 larly on the dorsal side, being little more than a thick glandular 

 layer, which constitutes the clitellum (Fig. 4). The unicellular 

 glands are here aggregated in sub-globular or pyriform groups 

 of from three to twenty or more, which extend inward to a 

 length of from .03 mm. to .065 mm. Being arranged in a 

 single stratum each cell forms part of the surface of the gland, 

 close to which lies the deeply staining nucleus, in a mass of 

 almost as deeply staining granular protoplasm. The inner 

 ends are granular but clear and often unstained, and pass into 

 ductules, which may be bound together into a fascicle, and 

 either open in close proximity on the surface, or separate and 

 open singly. In either case they wind a slightly spiral course, 

 which is best seen in living animals, particularly when stained 

 with methylene blue. The cell bodies have an average 

 diameter of .011 mm., the ductules of .0018 mm., and a total 

 length of about .05 mm. 



The several cells in each group appear not to function simul- 

 taneously. Some have completely broken down into secretion 



