THE ALIMENTARY CANAL. 51 



passing obliquely forward and others backward, and a set of 

 dorsal and ventral longitudinal muscles, the dorsal and ventral 

 recti. These two sets are antagonistic to each other, the 

 transverse fibres diminishing the diameter and increasing the 

 length of the larva, and the recti drawing the annuli together. 



The individual fibres and bundles of cutaneous muscles 

 would need many pages for the description of their origins and 

 insertions, and the details possess little or no interest. Lyonet 

 has already described the similar muscles of the caterpillar of 

 the goat moth ; I shall, therefore, content myself with a very 

 brief resume. 



Generally all the muscles are attached to the integument 

 where more or less obvious sulci are apparent externally, and 

 the muscles of each annulus are repeated in the others ; most 

 of the fibres pass from the edge of one annulus to that of the 

 next, but some pass over two or more without being attached 

 to the integument. 



The muscles of the cephalo-pharyngeal skeleton must be 

 regarded as an inflected continuation of the cutaneous sheet ; 

 the fibres and bundles of fibres are chiefly the continuation of 

 the recti : these form special retractors and protractors of the 

 fulcrum, or act upon the labium and the great hooks. The 

 great retractors of the fulcrum arise from the anterior edge of 

 the sixth somite, whilst the protractors arise from the forehead 

 and maxillae. This fact is a complete refutation of the view 

 held by Hammond,* that the delimitation of the several somites 

 can be determined by the insertions of the somatic muscles. 



In structure the larval muscles generally differ from those 

 of the imago, and they more nearly resemble the skeletal 

 muscles of vertebrates ; a detailed description will be given 

 in another chapter. 



6. THE ALIMENTARY CANAL, 

 a. Comparative Morphology. 



The Alimentary Canal in insects consists of four parts : the 



stomodasum and proctodaeum, developed from the epiblast ; 



* 'On the Thorax of the Blow-fly.' Journ. Linn. Soc. Zool., vol. xv., 1879. 



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