ORIGIN OF THE FORE AND HIND INTESTINE 547 



Fore-intestine (stomodaeum) and hind-intestine (proctodaeum) , Labrum. 

 The digestive canal of insects consists, as in other animals, 

 of three portions, the fore, mid, and hind gut or intestine. 

 The next change after the completion of the segments of the 

 primitive band is the development of the fore and hind intestine 

 and the appendages. The fore-intestine (stomodaeum) arises as an 

 invagination in the area of the primary head-section, and the hind- 

 intestine (proctodaeum) in the terminal section (Figs. 300 and 546). 



In insects generally the formation of the fore-intestine occurs earlier than 

 that of the hind-intestine. An exception was discovered by Graber and also 

 by Voeltzkow in Muscidae, where the proctodseum appears earlier. 



Usually at the time of origin of the stomodaeum a projection 

 arises at the anterior edge of the primary head-region, the so-called 

 fore-head (Fig. 527, vie), 

 which is the common rudi- 

 ment of the clypeus and 

 labruin. In many cases 

 (certain Coleoptera and 

 Lepidoptera) these rudi- 

 ments first assume the 

 form of paired hooks (see 

 Figs. 83, 102, 104, 105, of 

 Graber's Keimstreif der 

 Insekten, also Figs. 529 

 and 546), which after- 

 wards, by fusion in the 

 median line, become 

 single, though notched in 

 the middle; but in the 

 more generalized Blatta 

 and Mantis, as well as in 

 bees, the rudiment is sin- 

 gle at the outset. 



FIG. 527. Rudiments of the appendages of the em- 

 bryo of Hydrophilus : an, antenna ; md, mandibles ; 

 )!?!, 1st, ma- 2 , 2d maxilla; <ck, clypeal region; m, 

 mouth ; p 1 -}) 3 , legs ; p*-p 9 , rudiments of abdominal 

 appendages, 1-9; st, stigma; a, anus. After Heider, 

 from Lang. 



The view advanced by Patten, 

 and also by Carriere, that the 

 labruin is a first pair of an- 

 tennte, is scarcely tenable, and we quite agree with Korschelt and Heider in regard- 

 ing the clypeo-labral region as homologous with the upper lip of Crustacea, 

 and, we may add, of Merostomes and of Trilobites. 



It should be observed that in many insects, in their earlier embryonic state, 

 directly behind the mouth arises, from paired rudiments, what seem provisional 

 lower lip structures (not to be confounded with the 2d maxillae of insects). This 

 under lip structure was first discovered by Biitschli in the bee (his inner or 2d 



