168 MR W. E. HOYLE ON 



The annuli, however, are perforated by large pores or " stigmata," arranged 

 in from 6 to 8 irregular rows, but none of these are found in the interannular 

 spaces. 



These stigmata are about 0014 mm. in diameter, and almost circular in 

 form, and when seen en face present a double contour, which is due to the 

 difference in density of the cuticle immediately surrounding the stigma ; when 

 seen in section they appear very slightly constricted, so as to approach an 

 hour-glass in shape (PL XXVII. figs. 9 and 11) ; the cuticle immediately sur- 

 rounding the stigma is more highly refractile, and therefore probably also of 

 greater density than the other portions ; but there is no clear line of demarca- 

 tion between these as indicated by Leuckart in L. tcenioides* In some cases 

 the portion of cuticle around the stigma is slightly thickened, although this is 

 by no means constant. 



A surface view of the cuticle shows, moreover, a number of small irregularly 

 oval markings, arranged in fairly even rings around the pores, and producing 

 an appearance which recalls that of a transverse section of bone with its 

 Haversian canals and lacunae (PL XXVII. fig. 2). These marks are due to 

 the extremities of the epithelial cells, which form the next layer of the body- 

 wall, as was very distinctly visible in one small portion of the cuticle which 

 had this layer still attached to it. 



While treating of the cuticle it will be well to describe the hooks which are 

 modified portions of it. Their form is shown in the drawing (PL XXVII. 

 figs. 3 and 12) better than it can be described in words ; they are seen to be 

 composed of two separate joints, moved by appropriate muscles, which will be 

 treated of in the sequel. Their homology has been fully discussed by Leuckart 

 in his classic monograph, and my investigations have not enabled me to add 

 anything to what he has written upon this head. 



2. The Ejridermis, which follows immediately upon the cuticle, is a 

 single layer of columnar epithelial cells, 012 to 02 mm. in thickness (PL 

 XXVII. fig. 9, ep). The cells contain a distinct nucleus, generally oval in form, 

 and situated in varying positions in different cells ; in some cases a nucleolus 

 was visible. 



3. The Subepidermic Layer (PL XXVII. fig. 9, par) composes the greater 

 part of the body-wall of the animal. It varies greatly in thickness, but on an 

 average may be taken at 0*2 mm., the extremes being about 0*1 mm. and 035 

 mm. ; as a general rule, it is thinnest along the dorsal surface, and in the 

 narrow ventral intermuscular space (see p. 169) it is not unfrequently absent 

 altogether. 



The cells of which it is made up are of very various sizes and shapes ; 

 occasionally their diameter nearly equals the length of the epithelial cells, but 



* Loc. cit., p. 31, Tab. i. figs. 7 and 8. 



