340 Mary ß. Cravens aücl Harold Heath, 



type are globular in shape. The cells of the second class where 

 the epithelium is low are similar in form to the foregoing but where 

 it becomes high they assume a very slender vase-like shape. At 

 all points they are comparativly rare but may be recognized by 

 their secretion, reddish yellow aftei' treatment with haematoxylin, 

 and occasionally coarsely granular though usually the granules become 

 more or less confluent. 



In the mid line and at the sides of the animal and to a very 

 slight extent in the intermediate tract the epithelium is supplied 

 with sense organs which are represented in a typical condition in 

 Fig. 19. Each of these consists of an internal group of 3 or 4 cells, 

 of thick spindle shape and composed of almost homogeneous #j'to- 

 plasm containing a spherical nucleus twice the size of those of the 

 surrounding sensory cells. These latter elements are fully 25 in 

 number and although of essentially the same general character as 

 the solitary sense cells scattered over the body may be distinguished 

 from them by the more compact nucleus which stains darkly in 

 haematoxylin. All of these elements meet at the sui'face at a point 

 immediately surrounding the outer tips of the interior, possibly 

 supporting, cells, thus giving the organ a globular form. No especial 

 connective tissue sheath nor muscle fibres are attached to these 

 structures, the surrounding supporting cells holding them in place, 

 and although probably sensory no nerves have been found in their 

 immediate neighborhood. 



The basement layer, separating the epithelium from the under- 

 lying musculature, is approximately 0,0027 mm thick throughout the 

 body generally, although owing to the development of numerous 

 papillae (Fig. 19) serving to attach the epithelial cells, especially 

 in the head region, it may attain a thickness twice or three times 

 as great. Under high magnification it is clearly stratified but so 

 far as we have been able to determine lacks any cellular elements. 



The muscles of the body wall form two distinct divisions, an 

 outer circular sheet and an inner longitudinal layer of variable 

 thickness. The circular layer everywhere throughout the body is 

 relativly but slightly developed (Fig. 19j and is uniformly about 

 0,0054 mm in thickness. In the region of the cirri, which are lateral 

 outgrowths of the body wall, the circular muscles in the body become 

 highly developed (Fig. 18) and extend as longitudinal muscles 

 throughout the entire extent of each cirrus; but elsewhere there 

 are no especial developments. 



