

NO. 3 



INSECT HEAD SNODGRASS 



145 



(fig. 54 C) ; but in function the ventral muscles are probably accessory 

 to the dorsals by counteracting the pull of the latter on the press. 



It is difficult to discover a parallelism between the muscles of the 

 silk press in the caterpillar and muscles of the labium in other insects. 

 However, it may be possible that the two sets of muscles in the labium 

 of the grasshopper (fig. 40 D, 26, 2y) inserted on the salivary cup {v) 

 are the prototypes of the silk press muscles, though their insertion 

 points are ventral instead of dorsal. 



THE STOM ODEUM 



The stomodeum of the caterpillar (fig. 55) is diflferentiated into 

 four parts. The first part is a bucco-pharyngeal region {BuC, Phy) ; 



Cr 





BuC- 



^./ 



Fig. 55. — Anterior part of the stomodeum of a noctuid caterpillar, showing 

 muscles of the stomodeal wall, and the dilator muscles arising in the head. 



a-m, muscles of stomodeal wall ; BnC, buccal cavity ; Cr, crop ; OE, oesoph- 

 agus ; Phy, pharynx ; 20-23, muscles of buccal region, arising on _ clypeus ; 

 24-27, dorsal dilators of anterior pharyngeal region; 28-30, dorsal dilators of 

 oesophagus (posterior pharyngeal region) ; 31-36, ventral dilators. 



the second, a cylindrical tube with strong transverse muscle rings, 

 constitutes an oesophagus (OE) in the caterpillars, but it evidently 

 corresponds with the posterior section of the pharynx in Orthoptera ; 

 the third part is the large sack-like crop (Cr) ; the fourth is the con- 

 stricted posterior region of the stomodeum (fig. 56 F, Pvent), which 

 may be termed the proventriculus, though it has no special develop- 

 ment of the lining intima, such as usually distinguishes the proven- 

 tricular region in other insects. 



The muscular sheath of the entire alimentary canal of the caterpillar 

 is strongly developed, and in some parts becomes highly complicated 

 in structure. The alimentary muscles are particularly strong in the 

 noctuids, and the following descriptions are based mostly on Lyco- 

 photia margaritosa. 



