46 



PHYSIOLOGY OF THE INVERT EBRAT A. 



alimentary canal consists only of a short but wide oesophagus, 

 a large chylific ventriculus, and from four to six Malpighian 



tubules. There is no intestine 

 or anus. 



(12) The Coleoptera (beetles) 

 have masticatory mouths, and 

 the alimentary canal is framed 

 on the same type as the Ortho- 

 ptera ; but in the larval con- 

 dition of the Coleoptera the 

 gizzard is entirely absent. In 

 most herbivorous Coleoptera the 

 cbylific ventriculus of the larval 

 form is much shorter than in the 

 perfect insect or imago, and has 

 appended at both ends a num- 

 ber of CEecal tubes. But the 

 latter disappear during the 

 metamorpho sis . * 



" The alimentary canal is 

 most simple in the larvce of 

 insects in which, as in worms, 



Fig. 8. — Alimentary Canal of 

 Bee (Hymenoptera). 



: = oesophagus. i = honey-bag. 

 c ■— stomach, e = ileum. / = Mal- 

 pighian tubules. ^ = rectum. 

 i = valvular opening of stomach. 

 k = salivary glands. 



it usually extends, without con- 

 volutions, from one end of the body to the other ; in a few larvse, 

 as that of the bee, it has only the anterior opening or mouth, 

 and the opposite or anal orifice is not developed until the pupal 

 state. In all mature insects the alimentary canal presents 

 the two distinct apertures : it is simplest in the carnivorous 

 larviform Myriapodsf ; present more numerous and distinct 

 constrictions and divisions in the Hexapods, and increases in 

 complexity and length as the food requires most preparation 

 in order to effect its conversion into the animal nutrient 

 fluid." 



* With the exception of the genus Sister, for traces of these cseoal 

 tubes are to be found in the perfect insect, 

 t Not true insects. 



