ANATOMY OF THE NEMATODES 



263 



divided into four quadrants two dorsal and two ventral. The 

 elements of the dermo-muscular tube are in the simplest cases large, 

 rhomboid cells, that lie two by two in each quadrant, so that on 

 transverse section of the entire worm only eight cells are per- 

 ceptible. The outer border of the cells is converted into fibrils, 

 while the contiguous inner portion has remained protoplasmatic, and 

 contains the nucleus. In large species the muscular cells do not 

 only increase in length (up to 3 mm.) and in number in every 

 quadrant, but their contractile portion bends groove-like (fig. 182), 



FIG. 182. Diagram of a transverse section of 

 Ascaris lumbricoid.es, about 50/1. The flat intestine 

 is in the middle, and to the right and left near 

 it within the wall of the body the lateral ridges 

 with excretory vessel and lateral nerves, above 

 and below in the centre the dorsal or ventral 

 median ridges with the nerves radiating to the 

 muscles (after Brandes). 



FIG. 183. Anterior 

 end of an Ascaris mega- 

 locephala cut open and 

 showing the four tuft- 

 like organs lying on the 

 lateral ridges, natural 

 size (after Nassonow.) 



thereby even becoming larger ; simultaneously space is gained for 

 more cells, the protoplasmatic parts of such cells (on transverse 

 section) hang out of the grooves like vesicles. In all cases there 

 is only one layer of longitudinal muscular cells, which by con- 

 tracting can shorten the body, .or by contracting one side can 

 bend it. In the latter case the muscles of the opposite side 

 have an antagonistic effect, in the former the elasticity of the 

 cuticle acts in the same way. 



