NO. 8 MORPHOLOGY OF INSECT SENSE ORGANS SNODGRASS 



19 



described in following sections of this paper treating of the gen- 

 eral and specific structure of the sense organs ; this section will 

 deal with the cells of Type II. 



For convenience of description, the sensory nerve endings of 

 the body wall, and those of the alimentary canal will be described 

 under separate headings. Nearly all the axons of the nerve end- 

 ings of the body wall proceed to the ganglia of the ventral nervous 

 system ; those of the alimentary canal go both to the ventral gan- 

 glia, and to the ganglia of the stomatogastric system. 



Fig. 8. — Peripheral endings of sensory nerves on inner surface of 

 hypodermis. 



A, a subhypodermal multipolar sensory nerve cell of Type II (Cyll) 

 of a dragonfly larva with branches on articular membrane between 

 trochanter and femur (Zawarzin, 1912). B, part of subhypodermal 

 network of nerves from cells of Type II in larva of Mclolontha 

 (Zawarzin 1912 a). 



THE SENSORY INNERVATION OF THE HYPODERMIS 



In many soft-bodied larvse of insects there is an extensive net- 

 work of nerves on the inner surface of the hypodennis, which is 

 formed by the finely-branching terminals of the bipolar and multi- 

 polar peripheral sensory cells of Type II. This network (fig. 8 A, B) 

 constitutes the so-called subhypodermal plexus, though the fibers com- 

 posing it probably do not unite with one another. 



The extent to which this hypodermal iimervation occurs in differ- 

 ent insects, especially in adults, has not been determined ; it is known 

 to exist chiefly in soft-skinned larvae. A subhypodermal nerve net was 

 first noted by Viallanes (1882) in the larvae of Diptera (Stratiouiys, 

 Eristalis, Musca). It was described later in more detail by Monti 

 (1893, '94) in the larvae of Cerambycid beetles, by Holmgren (1896) 

 in the caterpillar of Sphinx ligiistri, by Hilton (1902) in the silk- 

 worm, and finally by Zawarzin (1912 a) in the larva of Mclolontha 



