NO. I THE INSECT HEAD SNODGRASS I3 



hypopharynx, and behind the latter is the opening (SIO) of the saH- 

 vary duct (SlDct). 



The hypopharynx is suspended by a pair of lateral rods (y) in its 

 wall that enter the head through the mouth angles and give attach- 

 ment each to a pair of muscles {13, 14). It is supported on the labium 

 by a pair of fulcral processes {hf) at the sides of the salivary orifice. 

 Between the suspensory rods the front surface of the hypopharynx 

 is somewhat depressed, and forms the floor of a pocket {Cb) of the 

 preoral cavity immediately before the mouth. This pocket has long 

 been called the "pharynx," regardless of the fact that it is outside the 

 mouth. Since it serves the cockroach at least as a receptacle for masti- 

 cated food to be swallowed, the pocket is now generally known as 

 the cibarium (Cb). It becomes the sucking pump of liquid-feeding 

 insects. Since, however, the cibarium was long ago called the 

 "pharynx," we still use the name "epipharynx" for the anterior or 

 dorsal wall of the preoral cavity (Ephy), and call the postoral lobe 

 the "hypopharynx." No one has yet proposed suitable names for 

 these parts. The true pharynx is an anterior part of the alimentary 

 canal (D, Phy). The salivary passage between the hypopharynx and 

 the labium (Slv) into which the salivary duct opens, may be termed 

 the salivarium. It is thus seen that the important parts of the insect 

 feeding apparatus lie entirely outside the mouth. 



An internal skeletal structure known as the tentorium is present in 

 the head of Thysanura and Pterygota. It consists of four apodemal 

 arms, two anterior and two posterior. The posterior arms are usually 

 joined to each other in a bridge through the back of the head, and in 

 the Pterygota the anterior arms are united with the bridge. The 

 points of ingrowth of the arms are marked by depressions in the head 

 cuticle termed the anterior and the posterior tentorial pits (fig. 4 A, 

 at; B, pt). The tentorium is highly variable in its structure and de- 

 gree of development, as will be described in a special section (p. 32). 



The position of the head relative to the body axis is variable. When 

 the face is directed forward and the mouth parts hang downward 

 (fig. 5 A) the head is said to be hypognathous. This should be the 

 primitive head position since the feeding appendages are modified 

 legs and thus have the same relative position as the thoracic legs. 

 The hypognathous insects are mostly vegetarians that live in the open, 

 feeding on the leaves, sap, or nectar of plants, though some are blood- 

 suckers. 



On the other hand, in many insects the head is turned upward on 

 the neck in line with the body axis (fig. 5B), so that the mouth 

 parts are directed forward, in which case the insect is said to be 



