of the proboscis. Wlien, as sometimes happens, the 

 proboscis is violently extruded and broken off at its attach- 

 ment the rhynchocoelom and rhynchodseiim form a con- 

 tinuous cavity until the proboscis is regenerated. The 

 rhynchopcplom contains a colourless corpusculated tlniil. 

 At its commencement between the rhynchocielom and 

 rhvnchodteum the proboscis consists of a layer of longi- 

 tudinal mnscle fibres covered externally l)y rhvnchocd^- 

 lomic and internally by pr()])oscidial epithelinm (PI. I., 

 fig. 4, p.). Just beneath the last layer are the two prolios- 

 cidial nerves. Further back the proboscis becomes con- 

 siderably thicker, and a layer of circular muscles makes 

 its appearance l)etween the longitudinal muscles and the 

 proboscidial epithelium. Fiom this circular layer at two 

 opposite poles, as seen in transverse section, fibres pass 

 throuffh the longitudinal lavei' to the basement membrane 

 just beneath the rhynchocoelomic epithelium, crossing one 

 another in two directions (PI. II., fig. (J, nirr.). In this 

 way are formed the so-called muscle crosses characteristic 

 of the Lineid proboscis. The crossing is more apparent 

 on one side than on the other. In this region also the 

 proboscidial epithelium is thrown up into papillae, and is 

 highly glandular, whilst just beneath it there is a com- 

 plete investing nervous layer which has been formed fiom 

 the two probo.<cidial nerves. Still further liack PI. II., 

 fig. 5), the nervous layer and the circular muscles 

 disappear, so that, except for the absence of the two pro- 

 boscidial nerves, the appearance of a section taken in this 

 region is somewhat similar to that of one taken near the 

 attachment of the organ {cf., PI. I., fig. d). 



The proboscis is attached by its hinder end to the dorsal 

 wall of the proboscis sheath about one-third of the length 

 of the animal from the anteiior end. This is effected by 

 the longitudinal muscles of the ])ioboscis being continued 



