30 THE VOYAGE OF H.M.S. CHALLENGER. 



specimens are so contracted that tentacles, oral disc, and upper part of body-wall were all 

 drawn inwards together; in the largest, however, part of the tentacular crown protruded. 



The surface of the body-wall is incrusted with sand-grains, so that at first sight 

 I was inclined to take the animal for a Sphenopics. The sand-grains are not, however, 

 embedded in the mesoglcea, but adhere to the cuticle of the ectodermal epithelium, so 

 that they can easily be removed by scraping. At the anterior end they are more 

 sparse, and are practically absent on the upper third. This part of the body-wall 

 assumes a different appearance to the rest, being more leathery or bark-like, and 

 traversed by rough longitudinal furrows. The bark-like appearance is produced by 

 the cuticle, which is strongly developed, and of a brownish tint, resembling that of 

 Phellia pectinata and Tealia hunodiformis. A fairly sharp boundary marks off from 

 the rougher part of the body-wall a strip about 1 cm. wide, which adjoins the oral 

 disc and wreath of tentacles, and which has a completely smooth surface. One can thus, 

 as in Halcampa claims, recognise three regions of the body, — capitulum, scapus, and 

 physa ; but only the capitulum is marked off from the rest with any degree of sharpness. 



Histologically the body-wall is composed of a strong fibrous connective-tissue. 

 The individual fibres are extremely fine, and are united in great numbers into tracts ; 

 they are not so sharply bounded, as, for example, in the connective-tissue of Verte- 

 brata, but, like them, have a curving course. Generally they cross one another and 

 interlace in every direction, and only under the endodermal surface does a longitudinal 

 arrangement preponderate, parallel to the endoderm. Here the fibres stain exceedingly 

 deeply in picrocarmine, while at all other points fine cords alone retain the stain 

 after washing. 



The endodermal circular muscle-layer is formed into lamellar pleats, arranged 

 closely like the leaves of a book, and seldom showing arborescence in section. A 

 muscular region specially developed for a sphincter is not present. 



The tentacles are small conical stumps, measuring in the contracted condition about 

 0"5 cm., and devoid of the two longitudinal ridges occurring in Halcampa clavus. On 

 the other hand, the terminal pores are obvious, and in many cases are recognisable 

 with the naked eye. The tentacles are arranged in several rows ; their number in one 

 case amounted to forty-six, and was perhaps increasing, as I found several small tentacles 

 among the larger. The longitudinal muscle lamella is ectodermal, and but little pleated. 



The oral disc is very small, and presents twelve radial ridges, produced at the 

 edge of the mouth into the longitudinal ribs of the stomatodasum ; the latter are 

 sharply-angled, with deep furrows between them. A specially differentiated siphono- 

 glyphe is not present. The length of the stomatodgeum in the largest example 

 amounts to nearly 2 cm. Correlated with the absence of a siphonoglyphe is that of 

 a stomatodeeal cone. The boundary between oral disc and stomatodreum is sharply 

 marked by the lip being elevated into a circular fold. 



