BULLKTIX: MrsP:UM OF COMrARATIVK ZOOLOGY, 



Integument. 



The body wall of the neraerteans consists of an outer integument, 

 composed of ciliated, glandular, and interstitial cells, and of a series 

 of two or more layers of muscles. 



The iiitegwaent is composed of highly columnar, often club- 

 shaped cells arranged irregularly in a single layer ; many of the 

 cells do not reach the surface, however, and others lie quite super- 

 ficially, these latter being attached among the underlying cells by 

 long fibrous processes (Text-fig. 1). 



The ciliated cells are commonly club-shaped and are covered on 



the outer, broader end with 

 numerous dehcate cilia. 

 The nucleus of each of 

 these cells is situated in the 

 narrowed neck of the cell 

 and well away from its free 

 border. The cell is com- 

 monly continued much fur- 

 ther beneath the nucleus as 

 a slender, root-like process, 

 which often twists about 

 among the bases of the 

 neighboring cells and ends 

 near the basement mem- 

 brane (Text-fig. 1, h). 



The glandular cells are 

 irregularly disposed among 

 the ciliated cells, and are 

 sometimes fewer and some- 

 times more numerous than 

 the latter. There are often 



Fri;. 1.— Diagram of cellular elements of integu- tWO Or more kinds of gland 



ment; a, «^ club-shaped glancl cells with coarse ^^ ■ ^^ ^ portion of 



granular secretion; h, goblet-shaped ciliated '^'^"^ ^" ""^ ° f 



cells; c, rod-like glands with clear, homogene- the body, and they may be 



ous secretion of verv firm consistency; d, basal -,. . „.,• i „ i ,^^t rM,l,r U\r 



cells for the replacement ..f overlying gland distinguished nOt onl) hy 



cells; e, unditterentiated basal cell; /, special- differences in shape and bv 



ized sensory cell with single cilium;n, nucleus. ^^^ ^aicrOSCOpic character of 



the secretion, but also by differences in their reaction towards vari- 

 ous stains. 



