626 



ZOOLOGY 



SECT. 



crystals containing uric acid are formed. These crystals afterwards 

 become absorbed ; their appearance and subsequent absorption 

 would seem to point to the probability that the fat-body is con- 

 cerned in separating out nitrogenous waste matters, which subse- 

 quently reach the exterior through the Malpighian tubes. Its 

 chief function is to serve as a reserve-store of nutrient material. 



Digestive system. Some Insects do not feed in the adult 

 condition, and when this is the case the mouth may be absent, 



FIG. 530. Digestive apparatus of 

 a Beetle (Carabus auratus). 



ad, anal glands : ab, their muscu- 

 lar appendages ; cd, stomach ; 

 ed, hind gut ; in, crop ; k, head 

 with mouth-parts ; ce. oasopha- 

 gus ; py. proventriculus ; vm. 

 Malpighian tubes. (From Lang, 

 after Dufour.) 



FIG. 531. Nervous, tracheal, and digestive systems of 

 the Honey-bee, a. antenna ; era, compound eye : b\, 

 b<2, b z , the three pairs of legs ; cm, stomach ; ed, hind- 

 gut ; hm, honey stomach (crop) ; rd, rectal glands ; st, 

 stigmata ; tb, vesicle of tracheal system ; vm, Mal- 

 pighian vessels. (From Lang's Comparative Anatomy.) 



as, for example, is the case in the Day-flies (Ephemeridce). When 

 a mouth is developed, as it is in the vast majority of Insects, it 

 is situated on the lower aspect of the head, bounded in front by 

 the labrum, and behind by the labium. It leads into the buccal 

 cavity or pharynx, into which open the ducts of a pair of salivary 

 glands, each of which often has associated with it a thin- walled 

 sac or salivary receptacle. Also in the neighbourhood of the mouth 

 in such larval Insects as spin a cocoon, the ducts of a pair of 



