146 BULLETIN OF THE 



(1) a posterior papillate zone ^ (z.pap.p.), (2) a smooth zone (2. levJ), 

 (3) an anterior papillate zone (z. pap. a.), and (4) the tentacular 

 crown (^pU. ta.). 



The posterior papillate zone occupies the posterior half of the intro- 

 vert, and shows a posterior portion, wliich is thickly studded with papillae, 

 and is dark brown in alcoholic specimens, and an anterior part much 

 lighter in color, where the papillae are somewhat scattered. The lightej-, 

 almost translucent appearance of the anterior portion of this zone, which 

 permits the centi'al mass of the oesophagus and retractors to shine 

 through as a dark band, is due to the great diminution in thickness of 

 the muscular layers. The line of demarcation between the lighter and 

 darker portions of this zone is somewhat definite, and is marked inter- 

 nally by the fusion of the longitudinal muscles into a continuous sheet, 

 and by the entrance into the body wall of the first large composite nerve 

 given off from the ventral nerve cord (r/. infra). 



The papillae of this region are all shaped like the bowl of a spoon with 

 the concavity directed toward the body and the tip posteriad. Adjacent 

 to the integumentary areas they are closely crowded, and overlap like 

 the shingles of a roof, so as to hide the skin completely. They vary in 

 size and shape, but are in general broadly pointed, measuring on the 

 average .25 mm. in length, and .65 mm. in breadth.^ Passing forward, 

 this general form is preserved until the point of transition from the dark 

 to the light portion of this posterior papillate zone is reached. Here the 

 papillae grow abruptly smaller in absolute size, though relatively longer 

 and narrower, until the characteristic mammiform papilla of the light 

 region is reached. These only are represented in Figure 1. They are 

 much lighter in color, and much less crowded, than the posterior papillae, 

 and leave irregular patches of skin entirely free. In breadth such a 

 papilla measures .25 mm. ; in length, .37 mm. I am unable to confirm 

 the statement of Andreae ('81, p. 205), that they are arranged "in 

 gleichen Abstanden"; for the relative distances are extremely variable, 

 being from 70 to 300 fx in the anterior portion of this zone. I was also 

 unable to find the arrangement in a double spiral reported by Yogt und 

 Yung ('88, p. 381). There seemed to be in fact no regular arrangement 

 common even to a majority of the specimens examined. 



Passing forward, the papillae gi-ow ever sparser, and finally terminate 

 along a well defined line, which marks the beginning of a smooth zone 

 (2. lev.. Fig. 1) entirely free from papillae. It measured 7 mm. in breadth 

 in a specimen which had an introvert of 4 cm. total length. Anterior to 



^ The posterior half of the posterior papillate zone is not shown in Figure 1. 



