344 Mary R. Cravens aud Harold Heath, 



layer, being almost wholly absent five sections posterior to the one 

 represented in Fig. 7. 



At a distance of about one third the length of the animal from 

 the hinder end of the body the proboscis sheath becomes more 

 circular, the lumen relativly larger and while the inner longitudinal 

 muscle sheath remains essentially unchanged the outer layer grows 

 thicker and more distinctly circular than in the mid section of the 

 animal. Neglecting the variations in the diameter of the canal, 

 which are illustrated in Fig. 1, 2, 9, the arrangement and relative 

 proportions of these layers remain unchanged throughout the 

 remainder of the sheath although there is a gradual diminution in 

 the amount of the constituent elements. 



In the extreme posterior end of its sheath a small portion of 

 the proboscis remains in position. As may be seen in Fig. 11 it is 

 bounded externally by an extremely thin endothelium, in which the 

 cell boundaries are invisible and the body of the cell very thin save 

 where thrown into prominence by the protruding elliptical nuclei. 

 Beneath this the longitudinal muscle layer is prominent, forming 

 fully half the thickness of the wall. A definite circular layer does 

 not exist in this part of the proboscis. However it may be said 

 that immediately anterior to the union of proboscis and sheath a 

 small but clearly marked circular band is present. Here and there 

 delicate fibres exist having more or less of a circulai- position, but 

 these appear in most if not all cases to be continuations of some of 

 the definite longitudinal bands. At the extreme posterior end of the 

 proboscis, which continues to be tubular to this point, the muscles 

 of its walls become continuous with those of one side of the sheath, 

 thus forming a retractor of very small size. An inner glandular 

 epithelium is present but the abundant secretion, within and without, 

 renders it impossible to determine the cell boundaries, the presence 

 of flagella and usually masks the nuclei which are basally situated. 

 No nerves were visible. 



Veeeill states (p. 448) that "the proboscis-sheath is well 

 developed and extends back nearly to the base of the tail where 

 it is abruptly narrowed to a short muscular band that joins the 

 walls of the body". In Nedonemerfcs pelagica the proboscis terminates 

 freely in the parenchyma immediately above the median division of 

 the intestine and there are no indications of any connection whatever 

 with the body wall. 



In its main features the digestive tract conforms to the hoplo- 



