382 MARGARET LEWIS NICKERSON. [Vol. XVII. 



upon a basement membrane,^ rises at frequent intervals above 

 its general level to follow the inner surface of the cuticula. 

 On the proboscis and tail it lines the cuticula covering the 

 papillae, while in the body region it follows the contour of the 

 excavations mentioned. Between the epidermis and the circu- 

 lar muscle is a quantity of loose connective tissue. Scattered 

 abundantly over the proboscis and body of the worm are found 

 the well-known epidermal organs which form the subject of 

 the present paper. On the introvert and tail these organs 

 occupy the papillae already described, while in the body region 

 they are partially included in the large excavations in the under 

 portion of the cuticula. They are ovoidal in shape; the 

 smaller end is directed outward, while the base rests upon 

 the circular muscle. 



The Epidermal Organs. 



The epidermal organs may be divided into two classes : one 

 containing gland cells, the other not. Each class may be sub- 

 divided into two types. The two types belonging to the first 

 or non-glandular class are distinguished by the presence or 

 absence of a bulb over the organ ; the two types belonging to 

 the second or glandular class by the presence or absence of 

 intracellular sacks in the gland cells. Each of the four types 

 contains sensory cells. Except in these organs I obtained no 

 indication of nerve cells or nerve terminations in the epithelium 

 covering the animal. Nerve endings are probably present in 

 the tentacles surrounding the mouth, but no observations upon 

 these structures are included in the present paper. Each 

 epidermal organ is flask-shaped and is surrounded by a deli- 

 cate membrane, probably an invagination of the basement 

 membrane, and in each type considerable variation is shown 

 in distribution and appearance, corresponding to the different 

 regions of the body in which they occur. For convenience, 

 the two types of non-glandular organs will be first consid- 

 ered, and afterwards the two types of glandular organs. This 



1 Andrews's statement, that no basement membrane is present, is certainly a 

 mistake, as a basement membrane can always be demonstrated in material which 

 has been well preserved and stained. 



