282 



AN INTRODUCTION TO ENTOMOLOGY 



they connect a very regular zigzag line ; such cross-veins are termed 

 gradate veins. Examples of series of gradate veins are well shown in 

 the wings of the Hemerobiidas and in those of the allied families. 

 The mouth-parts are formed for chewing. In several families the 

 larvas suck the blood of their prey by 

 means of their peculiarly modified man- 

 dibles and maxillae. These are very long 

 and those of each side form an organ for 

 piercing and sucking. The mouth-parts 

 of the larva of an ant-lion will serve to 

 illustrate this type of mouth-parts (Fig. 

 316). 



In this insect the mandibles (md) are 

 very long, curved at the distal end, fitted 

 for grasping and piercing the body of the 

 prey, and armed with strong spines 

 and setce. On the ventral aspect of each 

 mandible there is a furrow extending the 

 entire length of the mandible; and over 

 this furrow the long and slender maxilla 

 (mx) fits. On the dorsal aspect of the 

 maxilla there is also a furrow. These two 

 furrows form a tube which extends from 

 the tip of the combined mandible and 

 maxilla to the base of this organ where it 

 communicates with the mouth cavity. 

 Through this tube the blood of the prey 

 is conveyed to the mouth. On the middle 

 line of the body, between the mentimi (m) 

 and the front margin of the dorsal wall of 

 the head (/), there is a tightly closed slit 

 which is the mouth ; this, however, is not 

 functional, the food being received into 

 lateral expansions of the mouth-cavity at 

 the base of the mandibles and maxillag. 

 For a more detailed account of the struc- 

 ture of the mouth-parts of an ant-lion, see Lozinski ('08). 



The metamorphosis is complete. The larvae that are known are 

 predacious or parasitic and in most cases are campodeif orm ; a few 

 of them are aquatic, Sialidae, Sisyridaj, and certain exotic forms, but 

 most of them are terrestrial; some when full-grown enter the ground 

 and make earthen cells in which they transform, but most of them 

 spin cocoons. The silk of which these cocoons are made, in the case 

 of those in which the silk-organs have been described, is secreted by 

 modified Malpighian vessels and is spun from the anus. 



The silk-organs of Sisyra will serve as an example of netuopterous 

 silk-organs; these were described by Miss Anthony ('02). Figure 317 

 is a diagram of a sagittal section of a larva through the median plane. 

 In this larva the posterior fourth of the mid-intestine is merely a 



Fig. 316.— Head and mouth- 

 parts of a larva of an ant- 

 lion, ventral aspect: c, car- 

 do of the maxilla ;e, eye;/, 

 front margin of the dorsal 

 wall of the head, labrum 

 (?); m, mentum; m^f, man- 

 dible, mx, maxilla; p, la- 

 bial palpus; s, stipes of the 

 maxilla. 



