ec. 



'c.m. 



ZOOLOGY FOR MEDICAL STUDENTS CHAP. 



on its ventral side, towards its anterior end. This thicken- 



. Meiium it varies somewhat in position in different species 



mites XXXII-XXXVIl in L. he^deus, one of our 



,-thworms) .and as will be seen later it performs an 



,, n m connexion with reproduction. 



-wall of the worm is, as may be seen by examining trans- 



ulth the microscope, of complicated structure (Fig. 63). 



toderm or epidermis (Figs. 63 and 64, ec) a layer of 



elium, the individual cells of which are columnar in shape and have 



rficial layer of their cytoplasm condensed to form the cuticle 



sses uninterruptedly from cell to cell. Here and there may be 



seen a gland-cell its 

 cytoplasm laden with 

 drops of secretion, its 

 nucleus situated deep 

 down towards its inner 

 end, and its outer end 

 tapering off to a com- 

 l m paratively narrow tip 

 which is devoid of 

 cuticle. The cuticle 

 is thus incomplete, 

 or perforated by a 

 minute pore over each 

 gland-cell, so that the 

 secretion passes away 

 readily on to the outer 

 surface of the skin 

 which it serves to 



loist. Should the section pass longitudinally through a chaeta 



il may demonstrate the interesting fact that the chaeta 



i> -imply a small patch of cuticle enormously thickened so that it 



ts on the one hand outwards beyond the general surface and, 



>n the other, downwards into the thickness of the body-wall. The 



ing part of the chaeta is ensheathed in an epidermal 



the chaeta sac and the chaeta is in fact the cuticle secreted 



i mis forming the chaeta sac. Chaetae are liable to be worn 



1 . and in order to provide for this contingency a young reserve 



:med liy an outgrowth of the main chaeta sac (Fig. 64). If 



>i, the reserve chaeta commences to grow actively 



>on takes its place. 



IMC,. 64. 



e section of an earthworm passing through 



V.-jdovsky). c.e, Coelomic epithelium ; c.m, circular 



l.m, longitudinal muscles; m, 



muscle (or moving chaeta. [The cuticle is indicated by a thick 



