THYLUM NEMATIIELMINTHES 



cuticle (cu.}. It is wrinkled 

 transversely, so as to give 

 the animal a segmented ap- 

 pearance. Beneath the cu 

 tide is a protoplasmic layer 

 containing scattered nuclei 

 and longitudinal fibres, and 

 representing the ectoderm. 



Beneath the ectoderm is a 

 single layer vimuscvlarfibres 

 (m). of peculiar structure, 

 arranged longitudinally, and 

 bounding the body-cavity. 



The muscular layer is 

 not continuous, but is 

 divided into four longi- 

 tudinal bands or quadrants, 

 two dorso-lateral and two 

 ventro-lateral, owing to the 

 fact that at the dorsal, 

 ventral, and lateral lines 

 the ectoderm undergoes a 

 great thickening, and pro- 

 jects inwards, between the 

 muscles, in the form of four 

 longitudinal ridges. It is 

 this arrangement that gives 

 rise to the lines seen ex- 

 ternally. 



The mouth leads into 

 the anterior division of the 

 enteric canal, the pharynx 

 or stomodaeum (Fig. 76, 



