THE CATEHPJLLAII: IXTEUXAL ORGANS. 19 



verse eneireliiiu' hands. The small intestine is covered with hoth transverse 

 and longitudinal hands of thick, white and glistening muscular tissue ; at 

 its anterior end especially, where the alimentary canal is greatly constricted, 

 it is thickly covered with short longitudinal muscles, whose hinder extrem- 

 ities dovetail into other longer sets; hesides these, there arise fron) the 

 middle of the posterior end of the intestine a number of parallel bands of 

 nuiscular fibre, which embrace it diagonally, passing around to the ventral 

 surface of its anterior extremity ; starting just in front of the i)osterior in- 

 sertion of these, and interlacing with them at right angles, is another 

 shorter set of parallel nuiscles, whose other extremities are attached to the 

 body-wall ; still further, a set of four inde[)endent })arallel muscular bands 

 passes beneath and siii)ports the posterior end of the small intestine, reacli- 

 iny; horizontallv from the middle of one side of the eighth abdominal seo- 

 mcnt to the O[)posite. The colon is furnished simply with longitudinal and 

 transverse muscular bands, heavier than those on the stomach-wall. 



Digestive system. The digestive tract of the cateq)illars of butter- 

 Hies consists of an alimentary canal with anterior appendages (salivary 

 glands) and posterior appendages (biliary vessels). The alimentary canal 

 is a simple, straight, cylincbical tube, varied by expansions and contractions, 

 which divide it into an oesophagus (at the anterior extremity of Avhich the 

 salivary glands are emptied) , a long intestine, or stomach, if it may be so 

 termed, a short intestine (toward the anterior end of which the biliary 

 vessels are attached) and a colon. 



The oesophagus consists of two parts : anteriorly a simple, straight, 

 equal tube, and posteriorly a larger portion swollen in the middle — a sort 

 of "crop" — w'hich is better provided with muscular bands and extends part 

 way into the cavity of the second thoracic segment. The stomach is much 

 the more conspicuous portion of the alimentary canal and, indeed, the most 

 conspicuous organ in the body ; it is a straight swollen tube, always 

 crowded with food, and only occasionally larger in the anterior portion 

 because the animal has recently gorged itself; it extends from the middle 

 of the second thoracic to the middle of the seventh abdominal segment and 

 vai'ies in size according to the amount of food that has been swallowed ; 

 the walls seem to be the merest film, traversed by muscular fibres, which 

 by lines not deeply impressed divide the surface into narrow, rounded, 

 transverse, parallel lobes, reaching from the middle of the upper or the 

 under surface to the middle of either side and which alone prevent a per- 

 fectly free and direct movement of the fragments within. There is tdso an 

 in\'esting tunic of longitudinal muscles, and the two layers can readily l>e 

 separated from each other. This organ seems to act mainly as the recep- 

 tacle of the recently devoured food, since the fragments at the jxisterior 

 end seem scarcely more digested than those which have just entered the 

 anterior cxtremitv. At the middle of the seventh abdominal segment, or 



