ORIGIN OF HELICOID STRIAE 



391 



than one-third, and then again soon rather suddenly increasing a little 

 more than one-third, and finally is one-half, as wide as the corresponding 

 portion of the neck. The lining of the oesophagus is a rather distinct 

 feature throughout its length, and finds its main optical expression as a 

 somewhat sinuous axial element. The musculature of the oesophagus is 

 rather fine. Behind where the above-mentioned enlargement takes place 

 there is a considerable amount of granular matter in the oesophageal tissues. 



Fig. 3 Fig. 4 



Fig. 3. Helicoid striae of^Ascarophis helix considerably behind the middle of the 

 body. 



Fig. 4. Camera lucida drawing'of the contour of Ascarophis helix near the tail 

 end of a female. 



In front of this region the radial fibers are of a finer nature, closer together, 

 and the granulation much less apparent, if present at all; in other words, 

 there is a distinct change in the structure of the eosophagus at a point twice 

 as far back as the nerve-ring. The intestine becomes almost at once two- 

 thirds as wide as the body; it is separated from the oesophagus by a distinct 

 cardiac collum somewhat less than half as wide as the body. 





Fig. 5. Diagrams illustrating a theory of the mode of origin of helicoid striae through 

 anastomosing of the ordinary transverse striae of the nemic cuticle. Let 1 represent 

 seven ordinary annules of a nemic cuticle, and suppose the anastomosing to take place 

 on opposite sides of the nema at the places indicated by the arrows; 2 represents the 

 anastomosing as having taken place, precisely as indicated by the arrows in 1 ; while 

 3 and 4 show the further theoretical transition to perfect helices. It will be observed 

 that two helices are formed. Bilaterally symmetrical growth would necessarily lead 

 to helices of even number, as exemplified in Ascarophis. See also Figs. 6 and 7. 



