THE BECTAL PAPILLAE. 5? 



The large intestine is about four lines in length in the perfect 

 insect, but exceeds an inch in the larva ; it extends from the 

 openings of the bile tubes to a double muscular sphincter or 

 valve, which separates it from the rectum. It differs considerably 

 in structure from the small intestine. Its muscular coat, especially 

 the longitudinal fibres, is much more largely developed and its 

 middle or membranous coat is covered on its internal surface with 

 a number of sharp spines, with broad bases, which project down- 

 wards, and somewhat resemble narrow shark's teeth. These 

 processes become more blunt at the valve, between the large 

 intestine and the rectum, and extend into the upper portion of 

 that intestine; they afford an additional argument in favor of the 

 membranous coat being continous with the protoderni. Both the 

 large intestine and the rectum are lined with ordinary mucous 

 tesselated epithelium. 



The rectum dilates into a pyriform cavity, just below the 

 recto-colic valve, which contains the rectal papillae. Below this 

 dilatation it becomes again constricted, and a well developed 

 sphincter of circular fibres may be observed close to its outlet. 

 It opens at the upper part of the last joint of the ovipositor of 

 the female at its extremity, and in the male it terminates above 

 and behind the penis. 



The viscera may be carefully examined in situ, by partially 

 imbedding the insect in wax, and removing those parts of the 

 integument which are not imbedded, with a pair of fine scissors. 



Section V. The Rectal Papilla. 

 PLATE IV. Figs 9 to 12. 



The organs for which I have retained the name given to them 

 by Weismann, are four in number, situated near the termination 



