REPORT ON CEPHALODISCUS DODECALOPHUS. 19 



and the multitude of external apertures, thus suffice to place the little ciliated animals in 

 favourable circumstances as regards food, especially when the nature of their surroundings 

 is taken into account. 



Body-Wall 



In Rhabdopleura two layers of the body-wall were clearly distinguished by Professor 

 AUman, who had not the material aid which sections give the younger inquirers. 

 He called them ectocyst and endocyst, the latter " a very delicate membrane." Professor 

 Sars, subsequently, with fresh specimens at his disposal, denied that there was any 

 endocyst " (unless we consider the glassy skin, which closely surrounds the digestive 

 apparatus, to be an endocyst), consequently also no perigastric fluid." Professor Eay 

 Lankester, again, from the examination of living examples, recently observes of Rhabdo- 

 pleura that " the tissue which bounds the body-cavity consists of fusiform cells tapering 

 into fine fibres, sometimes branched." He further figures the structure of the body-wall 

 in optical and in transverse section, the coat formerly mentioned having within it 

 apparently a basement-membrane with ciliated enteric cells projecting from its inner 

 surface. In whatever way this form is considered, the structure of its body-wall very 

 much difi"ers from that of Cephalodiscus. 



I am unable from the mode of preparation of the examples (in spirit) to say much 

 about the pigment of the surface of the skin, but in some numerous specks of a reddish- 

 brown colour are still visible over the entire surface (PI. II. fig. 1) ; while, as already 

 mentioned, the buccal disk almost always presents the dull reddish band. In all 

 probability it is brightly tinted in life. In this respect it approaches the condition in 

 Balanoglosus ; thus Balanoglossus howalevslii has a white proboscis, a brilliant red-orange 

 collar with a whitish line round the operculum, while the rest of the body is orange-yellow. 

 Externally the surface is probably covered in life by a delicate ciliated cuticle, but 

 this cannot be diff"erentiated in the preparations. The same difficulty is met with in the 

 cuticular tissues of the Nemerteans. A decided difference is thus apparent between 

 Cephalodiscus and Loxosoma, in which the cuticle is considerably developed. What 

 remains is a well-marked layer of hypoderm (PI. VI. fig. 2, /i^) of the usual granular, 

 glandular structure. The coat just mentioned attains its greatest thickness at the base 

 and on the pedicle, but this may be partially due to corrugation from contraction. In 

 this layer are the numerous pigment-corpuscles and gland-cells, which latter do not readily 

 stain with carmine. It is bounded internally by a basement-layer, which is thin dorsally, 

 but better marked ventrally, especially behind the mouth, for the layer of longitudinal 

 muscular fibres now forms an additional coat in this region, and rests against the base- 

 ment-layer. Like the hypoderm the latter passes over the pedicle at the posterior end 

 of the body, and both are often thrown into wrinkles from contraction. The body-wall 



