10 W. BALDWIN SPENCER. 



This ridge is formed entirely of the outer layer, and stains 

 deeply. In longitudinal sections it is very clearly marked 

 (figs. 27, 29, R.). 



The thick inner layer, which, save in the region of the ridge 

 just mentioned, forms almost the entire thickness of the cuticle, 

 shows in sections the presence of great numbers of minute wavy 

 lines, as if it were composed of very thin laminse — an appear- 

 ance which may, however, be due to the action of reagents 

 (fig. 51). 



All over the head region and in the anterior half of each 

 annulus the cuticle is pierced by numbers of minute pores, 

 which form the stigmata, or the openings of very numerous 

 irregularly arranged glands. Each pore has a circular-raised 

 margin (fig. 31, st. gl.). 



The Cuticle-secreting Cells (fig. 51, E.). — These form 

 a continuous layer immediately beneath the cuticle. Each 

 cell is columnar (the average length is '035 mm.), and each 

 has a somewhat rounded, internal end, close to which is placed 

 a distinct nucleus. , The cells do not form a columnar epithe- 

 lium in the ordinary sense of the term, since they are not 

 uniformly closely apposed, but spaces are left between them, 

 through which pass to the cuticle the ends of muscle-fibres 

 and of special strands of connective tissue {W). There can be 

 no doubt that their function is that of secreting the cuticle. 

 In addition to this, groups of these cells are specially modified 

 to form the stigmatic glands, the description of which is given 

 under the head of excretory structures. 



4. Muscular System. 



(Figs. 24, 28—30, 32, 39, 51.) 



All authors agree in describing (1) a layer of circularly 

 disposed fibres, (2) a layer of longitudinally disposed fibres, 

 and (3) a layer of obliquely disposed fibres. In addition to 

 these, muscles are developed in connection with the alimentary 

 canal, the reproductive organs, and the hooks, which are some- 

 what dift'erently developed in different forms. 



