592 



ZOOLOGY 



SECT. 



found when we study its mode of development, to be a hcemoceelc 

 an extended part of the blood-vascular system. The coelome 

 is apparently represented only by the lumen of the reproductive 

 organs. 



A fat body is always present, either in the larval condition or 

 throughout life. It consists of a mass of polygonal cells bounding 

 the haBmocoele externally. When young the cells are nucleated 

 and possess a protoplasmic body. At a later stage a fluid loaded 



with minute granules takes the place 

 of the protoplasm, and crystals con- 

 taining uric acid are formed; these 

 crystals afterwards become absorbed ; 

 their appearance and subsequent ab- 

 sorption would seem to point to the 

 probability that the fat body is con- 

 cerned in the separating out of nitro- 

 genous waste matters, subsequently to 

 reach the exterior through the Mal- 

 pighian tubes. 



Digestive system. Some Insects 

 do not feed in the adult condition, 

 and when this is the case the mouth 

 may be absent, *as for example is the 

 case in the Day-flies (Ephemeridcc). 

 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, into which 

 open the ducts of a pair of salivary 

 glands, each of which often has asso- 

 ciated with it a thin-walled sac or 

 salivary receptacle. Also in the neigh- 

 bourhood of the mouth open, in such 

 larval Insects as spin a cocoon, the 

 ducts of a pair of spinning glands. A 

 projection of the roof of the mouth 

 cavity (epipharynx) is present in some 

 Insects; in others it is replaced by a projection from the floor, 

 the hypopharynx or lingua. 



The alimentary canal is nearly always considerably longer than 

 the body; it is longer in vegetable-feeding than in carnivorous 

 forms. The mouth leads into a long, narrow passage the oesophagus 

 (ce.) (Figs. 481 and 482) which dilates behind into a crop (in.) for 

 the storage of food. The place of this in sucking Insects is taken 

 by a stalked sac, usually termed the sucking stomach. The essential 



FIG. 481. Digestive apparatus of a 

 a Beetle (Carabus auratus). 



.</, anal glands ; rib, their muscu- 

 lar appendages ; cd, chylific ven- 

 tricle ; td, hind gut ; in, crop ; 

 '. I; head with mouth parts ; 

 ce. oesophagus ; p f . proventricu- 

 lus ; mi. Malpighian tubes. (From 

 Lang, afterDufour.) 



