STUDIES ON EARTHWORMS. 563 



the blood-vessels pass between the cells of the epidermis 

 (fig. 17, d), as in the Leech, and as Beddard has shown to be 

 the case in Perionyx and in Perichseta. 



The longitudinal muscles are arranged irregularly, as in 

 Microchseta, Allolobophora, and others. Connective 

 tissue is abundant, and forms a fairly thick layer between 

 the muscular layer and the coelomic epithelium. 



Previous writers have denied the existence of a clitellum ; 

 even Orley, who expressly looked for it, says that he has found 

 no trace of it ; yet in all my specimens, which are sexually 

 mature, a considerable difference in appearance is noticeable 

 behind somite xv, and extending to about somite xlvii. The 

 worm is here nearly cylindrical, though slightly concave on the 

 ventral surface, where the intersegmental grooves are not dis- 

 tinctly marked, but tend to run into one another across the 

 middle line as shown in fig. 10. The colour, at any rate in 

 spirit specimens, is rather darker over the dorsal and lateral 

 surfaces of this region than elsewhere. Noticing this, I cut a 

 series of transverse sections through the body, and I then 

 found that behind the somite xv the epidermis gradually 

 changed its character. 



In addition to the columnar cells forming the epidermis of the 

 general surface, a layer of elongated, club-shaped cells, of 

 various lengths, is present (fig. 18, c), so that the epidermis is 

 here some four or five times deeper than elsewhere, and deeper 

 at the sides than on the dorsal surface. These cells have a very 

 similar appearance to those in the clitellum of Lumbricus 

 and Microchseta, though they differ slightly in detail. Each 

 cell is filled with numerous highly refracting, small spherical 

 globules, and the protoplasm with the nucleus is confined, 

 apparently, to the inner, swollen end of the cell. As the cells 

 vary in length, the appearance presented is that of three or 

 four layers of such cells, as in Lumbricus; but in the latter 

 worm these club-shaped cells contain a granular substance, 

 and the rounded, refracting globules are confined to narrow, 

 elongated cells, intermediate in length between the club- 

 shaped and columnar cells and which are absent in Criodrilus. 



