BY VERA A. IRWIN-SMITH. 



789 



the body-wall is a thin, homogeneous layer, about 0*001 mm. thick 

 (Fig.28, cut.). An extremel}^ thin, dark line(/.), which, however, 

 becomes much thicker in the head, divides it from the next layer. 

 This is of about the same 

 thickness as the cuticle. It 

 is difficult to make out any 

 structure in it, but it appears 

 to be of fibrous composition; 

 and, lying along its inner 

 border, there are, at wide in- 

 tervals, elongated, oval nuclei 

 (71UC.). Below it, at about 

 equally spaced intervals, there 

 run four longitudinal bands 

 of mesoderm, containing nu- 

 merous, crowded, round nuclei 

 {d.m.b., and l.m.b.). These 

 bands are continuous from 

 the neck to the tail, and form 

 the innermost layer of the 

 body-wall. Within it is a 

 wide ccelomic cavity {cce/.), in 

 which lie the enteric canal 

 and the genital organs. In 

 the head, a loose sort of pro- 

 toplasmic tissue fills up a 

 great part of the cavity, be- 

 tween pharynx and body-wall. 

 Below the ventral body-wall, 

 in the region of the ventral 

 setae, there are four rows of block-like, finely granular masses, 

 staining deeply blue with hsematoxylin (PL xlvii., 6.771.). They 

 are quite separate from one another, about ten to twelve in each 



* Fig. 29. — L.S. through body-wall in region of ventral setae; ( x 950). 

 rig.29a. — T.S. in same region; ( x 610). The section has been flattened 

 out in cutting; v.s., bases of ventral setje. 



Figs. 29, 29a.— Ch. haswelli/ 



