NO. 4 FEEDING MECHANISM OF LEPIDOPTERA SCHMITT 



17 



Generalised structure. — In the more generalized insects there is 

 usually a large preoral cavity bounded anteriorly by the epipharyngeal 

 wall of the labrum and clypeus, laterally by the mandibles and the 

 maxillae, and posteriorly by the labium. The hypopharynx is sus- 

 pended between these organs (fig. 8 A, Pre) and thus divides the pre- 

 oral cavity into an anterior food meatus (fm), having the anterior 

 wall of the hypopharynx for its floor, and a posterior salivary meatus 

 (sm) enclosed between the posterior wall of the hypopharynx and 

 the anterior surface of the prementum. 



The food meatus, of course, is not part of the stomodaeum, but 

 simply space enclosed by certain mouthparts. It leads to the true 

 mouth which marks the beginning of the alimentary canal. A portion 



Mth Hphy 



Fig. 8. — Comparison of the orthopteroid head with the lepidopterous head. 



A, diagram of orthopteroid head (from Snodgrass). B, right half of head, 

 mesal view, of Danaus menippe, as exposed by median sagittal cut. 



of the food meatus just before the mouth is used to hold food before 

 swallowing and is therefore known as the cibarium (fig. 8 A, Cb). 

 The dilators of the cibarium always arise on the clypeus. 



The part of the stomodaeum just inside the mouth is termed the 

 buccal cavity (BuC). Beyond the buccal cavity, extending to the 

 cerebral nerve connectives, we may distinguish the pharynx (Pliy). 

 The dilators of the buccal cavity (dlbc) arise on the clypeus, but the 

 dilators of the pharynx (dlphy) arise on the frons. The frontal gan- 

 glion (Fr Gng) lies on the anterior wall of the stomodaeum between 

 the buccal cavity and the pharynx. The connectives of the frontal 

 ganglion (Fr Con) always pass laterad of the dilators of the pharynx. 

 From figure 8 A it may be seen that the pharyngeal dilators are thus 

 encircled by two nerve rings, outside of which they cannot migrate. 



