Class 3. Insecta. 



237 



The cliitinous cuticle in Insects is not calcified, but, not- 

 witlistanding this, it frequently attains a very considerable firmness, 

 and is often of great thickness ; below, there is an epidermis often 

 called hypodermis, usually a single layer of cells. In connection 

 with the skin, there are frequently skin -glands; of these may 



Fig. 198. Diagram of the principal anatomical points in an Insect. 1 — 3 first and 

 third pairs of legs out away, a anus, c cerebral ganglion, ch mesenteron, e prootodaeum, 

 g genital aperture, h heart, h crop, m mouth, n ventral ganglion, sp salirary gland, 

 •u, Malpighian tubule, ce ovary. — Orig. 



be mentioned, the stink-glands on the ventral side of the thorax, in 

 the Hemiptera ; the anal-glands of the Carabidse ; the wax-glands 

 of Apidse and of Cocci. Some are gland-cells, some true glands ; 

 sometimes they are represented by simple, flat, thickened portions of 

 the epidermis (wax glands of Bees). 



The nervous system is characterised by the great size to 

 which the cerebral ganglion often attains. The most anterior of the 

 ventral series, the s u b - 

 oesophageal, is situated 



in the head, like the cerebral A B Q 



ganglion, and gives off 

 branches to the mouth-parts. 

 This is succeeded by three 

 single or paired ganglia, one 

 for each thoracic segment, 

 and lastly, by a series of 

 abdominal ganglia. Often, 

 however, some of these fuse ; 

 the second and third thoracics 

 may, for instance j the pos- 

 terior abdominals also, or the 

 second and third thoracics 



Fig. 199. Nervous system of an 

 act (A), a cockchafer (JB), and a blue- 

 bottle (0). h cerebral ganglion, n 

 Bub-oesophageal ganglion, 1 — 3 the 

 three thoracic ganglia, u^ — 03 ab- 

 dominal ganglia, a fused abdominal 

 ganglia, sp passage for the oeso- 

 -After Brandt. 



