4 GUIDE TO CALIFORNIA INSECTS. 



it is called the scape. The next joint (pedicel) is usually separated from 

 the remaining joints (flagellum) by a hinge. 



2. Mandible, typically in the form of a somewhat curved cone, ending in a 

 point or with a number of teeth. The two outer angles of the base bear the 

 articular condyles and the soft skin of the basal articulation infolds at t^e 

 inner angle into a large tendon reaching nearly to the back or top of the head. 



3. Maxillae, appendages with very complicated and varying structure. 

 Typically consisting of two large segments (cardo and stipes) hinged together 

 and perhaps corresponding to the femur and tibia respectively, the latter 

 bearing the palpi corresponding to the foot but with structure more like an 

 antenna, and the lobes called galea and lacinia, the latter within and usually 

 sharp pointed or toothed. The stipes is often so divided as to have a sub- 

 galea from which the lobes arise and a palpifer bearing the palpus. 



4. Labium, almost identical in structure with the maxillae but usually 

 grown together forming a lower lip, and often with a less number of dis- 

 tinguishable parts. The terms mentum and submentum are commonly used 

 instead of stipes and cardo and these terms are not used with uniformity 

 in the different orders. 



Besides the four segments represented by the appendages, from one to 

 four additional segments have been considered by different authors as occur- 

 ring in the primitive head, the best marked of which is the preantennal and 

 the least evident the prelabial. 



After the appendages begin to develop as evaginations of the ventral 

 plate there begins an invagination at a point on the middle line at about 

 the suture between the mandibular and maxillary segments. This passes 

 between the commissures of the nervous system, dividing the ganglia of the 

 head into two sets which soon unite into two compound ganglia known 

 because of their position relative to this invagination as the supra- and 

 suboesophageal ganglia. 



At a later period a similar ingrowth from the hind end of the ventral plate 

 produces the intestines and just before the closing in of the back of the em- 

 bryo a third portion of the digestive tract is formed as a single layer 

 of cells which envelop the remains of the yolk and finally becomes the 

 stomach. Usually not until after the insect begins to feed are the walls 

 broken down between these three regions making the alimentary canal 

 continuous thru the body. 



Around the digestive tract a system of muscles are developed which by 

 constricting the tract from before backward forces the food along the canal. 

 Irregularity in the arrangement of these muscles and corresponding dif- 

 ferentiations of the cellular layer results in the division of the digestive 

 tract into a series of organs as follows: — 

 Stomodaeum. 



1. Pharynx or mouth cavity, often partly closed by the thickening of the 



