I'llYhUM A.WKLIDA •••^i 



Make a diagram, four inches in diameter, of a cross-section 

 showing the features described above. Do not represent the 

 cell structure. 



Having ubliiined a j^t'ncral idea of tlu' cross-section, study it 

 with the low power or if necessary the high power for detailed 

 structure. Note the following features of the body wall from 

 without inward: (1) ii very thin nitirlc or non-ccUular covering; 



(2) the epidermis, consisting of a single layer of cells, among 

 which numerous glattd cells may be distinguished by their oval 

 shape and swollen appearance; (3) the inuscular layers, consisting 

 of a thinner layer of very long, slender, circular muscle cells 

 embedded in connective tissue and attached to the septa, the 

 longitudinal layer of muscle cells which when seen in cross-section 

 appear feather-Uke; (4) the peritoneum, a thin layer of flat cells 

 lining the body cavity and attached to the inner surface of the 

 longitudinal muscle layer. 



The intestinal wall shows the parts arranged in layers. Some 

 of these layers, notably the longitudinal muscle and vascular 

 layers, are inconspicuous and made out with difficulty, hence may 

 be omitted from an elementary study. The evident layers are : 

 (1) the peritoneum on the outer surface, comprising large yellow 

 cells called the chlorogogen cells; (2) the circular muscles, a thin 

 but continuous layer of circularly arranged muscle cells; and 



(3) the lining epithelium, or the innermost single layer of elongated 

 ciliated cells. 



In a sector of the diagram previously drawn show the details of 

 cellular structure of the body and intestinal walls. 



Nerve Cord.~The nerve cord is somewliat oval in outUne and 

 is covered externally by a sheath, consisting of peritoneum, 

 connective tissue, mu.scles, and blood vessels. The subneural 

 blood vessel on the midvcntral side and the paired lateral neural 

 blood vessels, one on each side of the subneural vessel, can be 

 distinguished under high power. In the dorsal portion of the 

 cord are three large, clear areas, the giant fibers, which extend for 

 long distances in the worm. I^ach is surrounded by a thick 

 sheath. If the section happened to pass through a ganghon of 

 the cord a number of large nerve celis may be present. The rest 

 of the cord is made up of numerous small nerve fibers forming a 

 network. 



Make a drawing, one and one-fourth inches in diameter, of a 

 cross-section of a nerve cord. Show in detail the structures 

 described above. 



