TYPHLORHYNCHUS NANUS. 643 



The fcpitlielium lining tlie lumen {Ph. E.) is very much 

 reduced, excepting at the lower end of the pharynx, where 

 it is continuous with the epithelium on the exposed surface. 

 It is quite devoid of nuclei (cf. Mesostomum Cuenoti). 



In addition to the intrinsic muscles of the pharynx a large 

 number of fibres run fi'om the body-wall to become attached 

 to its anterior wall, apparently fusing with the outer longi- 

 tudinal fibres of the pharynx itself. It is the insertion of these 

 fibres into the body-wall which causes the constriction that 

 cuts ofE the proboscis from the rest of the body (fig. 4, A. 31.). 



There is no well-marked oesophagus ; a few unicellular 

 glands lie in the neighbourhood of the upper end of the 

 pharynx. 



The gut is spacious ; posteriorly it extends as far back as 

 the level of the female aperture. That part of it running 

 into the proboscis is best described as an anterior unpaired 

 diverticulum (fig. l,A.d.). This diverticulum is often occluded 

 to a considerable extent by pseudopodial processes sent out 

 by the endoderm, but can always be distinguished in trans- 

 verse sections. The characters of the endoderm have been 

 sufficiently described in dealing with the parenchyma. 



Nervous System. — The brain lies in the proboscis at 

 about its middle, and consists of a quantity of ganglion cells 

 (fig. 5, G.) lying about a transversely elongated mass of 

 " Puuktsubstanz," apparently composed of exceedingly fine 

 fibrilla) (tig. 5, br.). 



The Punktsubstanz, or central mass, is divided into two 

 lobes by a slight median constriction, and from each of the 

 lobes a group of nerve-fibres runs outward for a short 

 distance towards the wall of the proboscis, and then turns 

 backwards (fig. 5, N.). A group of fibres also runs from the 

 ganglion cells lying in front of the central mass to each lobe 

 of the latter close to the middle line, and a similar group of 

 fibres passes into the central mass from ganglion cells lying 

 behind it. These posterior fibres do not form such compact 

 groups as the anterior pair, and enter the central mass more 

 latei'filly. 



