232 



THE BRITISH NATURALIST. 



[October 



We have seen that the most important elements of the mechanism 

 by which actions result from external stimulation are : — - 



(1) A sensitive area. 



(2) A nerve connecting this with a nervous centre. 



(3) A nervous centre. 



(4) A_ nerve joining this centre with a muscle. 



(5) A muscle or simpler contractile element. 



In the lower animals, although the action in response to stimuli 

 is present, there is no differentiation of their structure, and any 

 portion of the body is capable of taking the place of these five 

 elements. 



As we advance to higher forms, the first element appears as a special 

 structure, and with it the fifth. The second, third, and fourth elements 

 are. still undifferentiated, and this condition we find in Vorticella or in 

 Hydra. In higher forms still we find all the five represented. This 

 condition appears in some of the lowest worms, and frotn this condition 

 to that found in the highest animals the change is only in the degree of 

 elaboration of these five elements. More especially does the elaboration 

 of the nervous centre increase ; in fact, it is by its development 

 especially that there results that greater use of the sense organs, that 

 greater power of appreciating conditions in the surroundings and 

 re-acting properly to them, which distinguishes the higher from the 

 lower forms of life. 



AN ENTOMOLOGICAL VISIT TO THE CANARY 



ISLANDS. 



BY G. MOREL-DEVILLE. 



To make this paper in any way interesting, considering the very 

 short period I remained in Canary, and the consequent little time at 

 my disposal to collect and investigate the various forms of insect life 

 abounding in that island, I am afraid I must touch upon other 

 subjects besides " entomology." Indeed, if I confined myself 

 exclusively to that interesting study a few lines w r ould suffice to detail 

 my experiences, in which case it would hardly be worth while to take 

 up your space. However, it occurs to me that .a general description 

 of the country, with the various objects of interest it contains, might 

 prove to a certain extent acceptable. I have acted upon this, but 

 as far as possible I have confined myself to Natural History. 



