NO. 4 FEEDING MECHANISM OF LEPIDOPTERA SCHMITT 3 



of the postoccipital suture, the posterior tentorial pits appear to be 

 " higher " in the lepidopterous head than they are in most other insects. 

 Internally, this part of the hypostomal suture is marked by a well-de- 

 veloped ridge, on which are inserted the ventral intersegmental muscles 

 from the thorax. The postocciput and the posterior part of the hypo- 

 stoma are either poorly developed or entirely membranous. 



The ventral areas of the parietals are not marked ofi from the sub- 

 genal areas by sutures, so it may be said that the pleurostomal and 

 anterior part of the hypostomal sutures are nonexistent. Since the in- 

 vaginations of the anterior tentorial arms of pterygote insects are 

 always found in either the pleurostomal or the epistomal sutures, it 

 might be supposed that the furrow extending ventrally from each 

 anterior tentorial pit is the pleurostomal suture. Such, however, is not 

 the case. This deep infolding is the line along which the clypeus and 

 the parietal have been brought into juxtaposition, so that the true 

 pleurostomal suture would necessarily be within the infolded area. In 

 some groups, as in the Tineidae and the Pyralidae, this infolding is 

 not pronounced, but in the butterflies it is extremely well developed. 

 From a practical viewpoint, these infolded ridges are continuous with 

 the ridges that brace the floor of a sucking pump, and will be de- 

 scribed later. 



The cephalic endoskeleton, or tentorium, of moths and butterflies 

 presents practically the same structure throughout the order (fig.i A). 

 The anterior arms of the tentorium are well developed and are the most 

 important part. They are without dorsal arms, and the antennal 

 muscles arise directly on them. The anterior arms are attached to the 

 posterior bridge, close to the invaginations of the posterior arms. In 

 many cases the actual posterior tentorial pits are really large open 

 depressions, so that when seen from the inside of the head the anterior 

 arms and the tentorial bridge appear to have separate invaginations. 

 The posterior bridge is always small and poorly developed, and no 

 muscles actually arise on its span. 



The only muscles arising on the anterior arms of the tentorium are 

 the antennal muscles and two pairs of muscles affecting the extension 

 of the proboscis, which will be described later. In the butterflies and 

 in moths having functional mouth parts the tentorial arms are often 

 provided with large flanges and ridges, to allow greater attachment 

 surface. In moths having degenerate or obsolete mouthparts the ten- 

 torial arms are often bulging and thin-walled, especially in the anterior 

 halves. 



The foramen magnum is sharply constricted near the invaginations 

 of the posterior tentorial arms, although the degree of constriction 



