INSECTA 121 



occupies the region of the head between the oesophagus arid 

 the epicranial wall, and it' is supported on a chitinous ingrowth, 

 the tentorium. The two large fused ganglia of the brain 

 are produced into optic and antennary lobes on each side, 

 and these supply the nerves to the eyes and the antennae 

 respectively. Circum-oesophageal commissures connect the 

 brain with the sub-oesophageal ganglia, which are also fused 

 and supply nerves to the mouth appendages. These ganglia 

 are the first of the ventral chain of ganglia, which is made up 

 besides of the three thoracic ganglia, one to each segment 

 of the thorax, and the six abdominal ganglia situated in the 

 first six segments of the abdomen. The last of the series 

 supplies nerves to its own and all the remaining segments. 

 The successive pairs of ganglia are connected by double 

 commissures. 



A visceral nervous system arises from the circum- 

 oesophageal commissure as a pair of nerves which unite above 

 the oesophagus in a ganglion, and, running backwards over the 

 crop, the nerve is joined by a pair of nerves issuing from the 

 brain. The course of these nerves is easily followed on the 

 crop. 



The nervous system in insects is in a highly developed 

 condition, and associated therewith the nervous activities 

 are of a high order and have often been discussed by the 

 naturalist and by the student of animal behaviour. The nerves 

 are spread to all parts of the body and ramify in particular 

 in the skin. They thus bring into intimate association all 

 parts of the body. It has been shown also that the ventral 

 ganglia are capable of inducing automatic movements apart 

 from the brain. 



Special sense organs are developed : the antennae, which 

 are tactile and olfactory ; the eyes ; the cerci, which appear to 

 function as posterior tactile organs, and tactile cells with setae 

 throughout the skin. 



The eyes are like those of the lobster, and consist of a large 

 number of closely adpressed hexagonal facets, or ommas, derived 

 from the ectoderm, separated by upper and basal masses of 

 pigment. Each consists of a transparent cornea and crystalline 

 cone, a long rhabdome surrounded by the retinula, and the 



