76 ARTHUR E. SHIPLEV. 



in the middle of the body they are, however, ahnost entirely 

 confined to the dorsal surface. These papilla; are shown in 

 fig. 11. 



The colour varies in different specimens. The ground 

 colour is always yellowish-brown, with a peculiar iridescence, 

 noticed by other observers : on this are patches of a black or 

 deep brown pigment, which are generally so arranged as to 

 form a few irregular rings in the middle of the introvert and 

 smaller patches on the anterior dorsal part of the trunk. 

 Individuals are, however, found in which the pigment is only 

 very slightly developed ; while in others the whole dorsal 

 surface of the body is thickly mottled with dark patches. 



The body wall is everywhere covered by an ectodermal 

 epithelium, one cell thick. The characters of the cells pre- 

 senting marked differences in different regions. 



The ectoderm covering the lower lip and the outer 

 grooved surface of the tentacles is columnar and covered with 

 short thickly set cilia (figs. 4 and 8). 



The prseoral lobe, together with the inner surface of the 

 tentacles, is covered by a layer of cubical cells, the outer half 

 of each cell in this region being loaded with granules of a dark 

 brown pigment (figs. 4, 7, and 8). These cells are not ciliated. 



The epithelium covering the collar is formed of short 

 cubical cells, which appear to become more flattened when this 

 organ is extended (fig. 4). 



On the remainder of the introvert the ectoderm secretes, 

 except in the region of the hooks and papillae, a clear homoge- 

 neous cuticle 0"02 mm. thick. 



Each hook is secreted by a raised papilla, which projects 

 into the cavity of the hook. The cells covering the papilla 

 being large and cubical, provided with conspicuous spherical 

 nuclei (fig. 21). 



Behind each hook is a small organ, apparently sensory, 

 which will be described below. 



The ectoderm of the trunk consists of lamellar, dome-shaped 

 cells, secreting a thick cuticle almost 04 mm. in thickness 

 (fig. 13). The outer surface of this cuticle is rough and 



