608 MEMOEY OF INSECTS. 



nervous mechanism for the larva state has been shown in Fig. 126 ; for 

 the pupa, 127 ; for the imago, 128 ; from which it will be recognized 

 that the nervous system of insects, as they pass through their metamor- 

 Changes in the phoses, undergoes change. In the larva state, the nerves, as 

 nervous system they branch forth from the ventral cord, indicate by their uni- 

 mTtTmorp^o- formity the equality of the segments of the body. In many 

 sis - cases the cord is separated throughout its whole length into 



its two constituent strands, and the cephalic ganglia are minute because 

 of the imperfect condition of the organs of sense. In the .pupa state 

 there is a general approach of the ventral ganglia, an increase of the 

 cephalic, and a thickening of the strands which connect that organ with 

 the suboesophageal. In the imago state the cephalic ganglia have still 

 farther increased to a size which corresponds to the great development 

 of the organs of sense ; the ventral ganglia appear to have coalesced in 

 the thorax. The general result of these changes during metamorphosis 

 is therefore to effect a concentration of the nervous centres in the head 

 and in the thorax, the ganglia of special sensation coalescing in the for- 

 mer, and those of motion in the latter region. We may remark that 

 these modifications strikingly illustrate the observation that change in 

 habits of life is always preceded by change of the nervous system. 



Besides being the repository of the impressions of the special senses, 

 Seat of mem- tne cephalic ganglia discharge a function of a more general 

 ory in insects. an c[ most important kind, since doubtless they are the seat of 

 memory. That insects of the more elevated kind have the power of 

 recollection there can not be any doubt. If there were no other fact, 

 their recognition of their homes would be sufficient to establish this. A 

 thousand trivial incidents offer indirect, but instructive and interesting 

 proofs of the same thing. When a spider who has been disturbed feigns 

 death in order to avoid the cause of his alarm, he proves his capacity of 

 recollection, as also when he has been brought out from his concealment 

 by touching his web, and, discovering the nature of the imposition that 

 has been practiced upon him, refuses to come forth upon a repetition of 

 the trial. The quality which the cephalic ganglia thus possess of bear- 

 ing upon themselves the enduring traces of impressions received through 

 the sensory organs scarcely requires here to be more particularly exam- 

 ined. In the preceding book, in the chapter on inverse vision, various 

 facts have been mentioned which illustrate the faculty possessed by the 

 optic centres in man of retaining visual impressions for a considerable 

 period of time ; as, for instance, if, when we awake in the morning, our 

 eyes are directed to the bright window and then closed, a representation 

 thereof will still continue to be seen in its natural colors and relations, a 

 representation which gradually fades away; and, in like manner, the 

 cephalic ganglia register the impressions they receive from the optic, 



