86 



ftpecialisp<l ninonjj; tlie Cyelol)rrtnc'h Docoftlossa. and tlifrelty 

 g'ives evideiu'e of tlie difticiilty of dig-estiiig the ioiigdi 

 vegetable food ; tlie liigli development of folds must also 

 enable this region of the g'uf to act as a strainer, preventing 

 the further transport of large fragments into the thiu 

 walled regions Avhieh follow. Tbe o-reat leno-th and size 

 of the stomach, which is the region where the secietion of 

 tlie e-reat dig'estive o-land becomes mixed with the food 



O O o 



is a further testimony to the slowness and difficulty of llie 

 digestive process. 



Xervous System and Sexse ()r(;axs. 



The nervous system of Pdtelhi nih/afa (fig. 2-)) may be 

 considered under three headings. 



(a) The rUrcumoesophageal ring with its cerebral, 

 pleural and pedal ganglia, and the principal nerves thence 

 given off except — 



(J)) The liuccal and Labial nervous systems, connected 

 to the ring at the cerebral ganglia. 



(c) The Visceral Loop and nerves thence given olf, 

 connected to the ring at the pleural ganglia. 



The fire u m oe s o p h a g e a 1 1{ i n g. This is 

 seen, after exposure of the dorsal surface of the gullet, 

 on pressing apart the gut tissues and bod}^ wall in the 

 region of the head and neck. When comjiletely exposed 

 it is observed to be roughly four-sided, the plane of the 

 quadrilateral sloping downwards and backwards, while 

 its u])per and lower sides are curved outwards. Tlie 

 fiuadrangular form of the ring is duo to its havin.g accom- 

 modated itself to the outlines of the buccal mass. Though 

 ceitain swelling's on the rinff are referred to as oano'lia, 

 it must not be supposed that nerve cells aie not found in 

 other parts, the concentration of these being by no means 

 (•om])lei(\ The two up|)cr corneis of th(^ (|nadi'ihilcr;il 



