46 



PHYSIOLOGY OF THE INVERT EBRATA. 



alimentary canal consists only of a short but wide oesophagus, 

 a large chylific ventriculus, and from four to six Malplghian 



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- j 

 ]?tcra ; but in the larval con- 

 dition of the Goleoptcra the . 

 gizzard is entirely absent. In ' 

 most herbivorous Colcoptcra 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 c^cal tubes. But thel 

 latter disappear during the 

 metainorphosis.* 



""The alimentary canal is| 

 most simple in the larva: oj 

 insects in which, as in worms,! 

 it usually extends, without con- 

 volutions, from oue end of the body to the other ; in a few larvae, I 

 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 I 

 constrictions and divisions in the Hexapods, and increases in 

 complexity and length as the food requires most prepai-ation j 

 in order to effect its conversion into the animal nutrient 

 fluid." 



* With the exception of the genus Hister, for traces of these c»cal 

 tubes are to be found in the perfect insect. 

 f Not true insects. 



Fig. 8. — Ali.mkxtaky Can".\l of 

 Bee {Hymenoptera). 



a = oesophagus. b — honey-bag. 

 c — stomach, e = ileum. /= Mal- 

 pighian tubules. er — rectum, 



z = valvular opening of stomach. 

 k = salivary glands. 



