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TEXT-BOOK OF ENTOMOLOGY 



B 



be regarded as an intussusception of the oesophagus. While in the 

 embryo the invaginated portion of the oesophagus is short, after the 

 hatching of the larva it projects backwards into the mid-intestine. 



Kowalevsky also observed in 

 a young muscid larva, 2.2 mm. 

 in length, that the oesophagus, 

 shaped like a tube, extends 

 back into the expanded por- 

 tion (p r o v e n t r i c u 1 u s) and 

 opens into the stomach (Fig. 

 315, A). In a larva 10 mm. 

 long the funnel is shorter, the 

 end being situated in the pro- 

 ventriculus (Fig. 315, ,>?). In 

 the cavity between the outer 

 (p) and inner wall (f) no food 

 enters, and the use of this 

 whole apparatus seems to be 

 to prevent the larger bits of 



FIG. 315. CEsophapeal valve of young muscid larva: food from passing illtO the cliy- 



i, its opening ; /, thickening of tlie cells ; i>tes, uieso- 

 derm. -Afte? Kowalevsky. 



i 

 stomach 



Beauregard has found a similar structure in the Meloidse, and calls it the 

 "cardiac valvule" (Fig. 318, 7i7). It was observed by Mingazzini in the larvae 

 of phytophagic lamellicorn beetles, and Balbiani described it in a myriopod 

 (Cryptops) under the name of the " cesophageal valvule." 



Gehuchten describes a homologous but more complicated structure in a 

 tipulid larva (Ptychoptera contain! nata), but differing in containing blood- 

 cavities, as a tubular prolongation of the posterior end of the oesophagus which 

 passes through the proventriculus and opens at various positions in the anterior 

 part of the chylific stomach (Fig. 31(5). 



The three layers composing this funnel are distant from each other and 

 separated by blood-cavities, the whole forming " an immense blood-cavity 

 extended between the epithelial proventricular lining and the muscular coat." 



According to Schneider the longitudinal muscular fibres of the fore and 

 hind gut in insects pass into the stomach (mid-gut). The anterior part of the 

 f< ire-gut has generally only circular fibres. When, however, the longitudinal 

 fibres arise behind the middle, then they separate from the digestive canal and 

 are inserted a little behind the beginning of the chylific stomach. Hence there 

 is formed an invagination of the proventriculus, which projects into the cavity of 

 the stomach. 



Schneider describes this process, which he calls the "beak," as an invagina- 

 tion of the fore-stomach which projects into the cavity of the stomach. The 

 two layers of the invagination in growing together form a beak varying in shape, 

 being either simple or lobed and armed with bristles or teeth. This beak is 

 tolerably large in Lepisma, Dermaptera (Forficula), Orthoptera, and in the 

 larv?e and adults of Diptera, but smaller in the Neuroptera and Coleoptera, 

 while in other insects it is wanting. 



