156 



SCOLECOLEPIS VULGARIS, 



ventral longitudinal muscles are nearer each other. The attachments of the oblique in 

 this region are at the upper and outer part of the nerve-area, whilst over the area 

 internally are transverse muscular fibres, to which are attached the fibres from the gut, and 

 in the centre of which is the ventral vessel. On each side of the vessel and touching the 

 circular layer is a band of longitudinal fibres (Fig. 115). The gut is richly folded 

 internally, the folds in section having the cells arranged in a pennate manner. 



In Scolecolepis cirrata, Sars (Fig. 116), the situation of the central ganglia corre- 

 sponds with the preceding, and the nerve-cords follow the progress of the oblique 

 muscles toward the ventral surface, each trunk having a small neural canal. The 

 dorsal region of the snout forms a conspicuous mass of the hypoderm in vertical 

 sections in a line with the mouth and the first bristle-bundles, and the lateral 

 areas anteriorly are highly vascular. When the body-wall is completely formed, e. g. 

 at a quarter of an inch from the snout, the size of the longitudinal muscles is conspicuous. 

 The dorsal, which at first are somewhat lateral in position, by-and-by form a thick 

 superior arch, and proceed a considerable distance down the lateral wall; whilst the 

 vertical muscles constitute two large curved masses in transverse section, the inner border 



onv t^-C vm 



Fig. 116. — Transverse section of the anterior region of Scolecolepis cirrata, Sars. 



of each being so carried upward that a deep ventral sulcus is formed for the nerve- 

 trunks and their thick hypodermic investment. The attachment of the strong oblique 

 muscles on each side of the mid- ventral line also aids in drawing up the mid- ventral 

 region. The rounded, firm nature of the alimentary canal gives little scope for the 

 development of the vertical fibres. 



Posteriorly the trunks still remain hypodermic, the ventral median line being 

 indicated by a flat ridge of that tissue. The ova in this species are very large, and 

 have a thick, minutely punctate zona. 



1. Scolecolepis vulgaris, Johnston, 1827. Plate XC, figs. 3, 4, and 5; Plate XCVII, 

 figs. 3 and 3^— feet; Plate XCVIII, fig. 2— head; Plate CV, figs. 2 and 2b— 

 bristles and hook ; Plate XCIV — ovum. 



Specific Characters, — Head truncate, with a frontal tentacle at each side, the anterior 

 border forming the base of a triangle, the apex of which goes to an adherent occipital 



