714 RECORD OF CURRENT RESEARCHES RELATING TO 



(b) On tlie presence of the supra-oesophageal ganglion depend (1) 

 tlie spontaneous activity of the animal as a whole, or what might be 

 called its volitional activity ; (2) the power to inhibit the aimless 

 and wasteful mechanical activity of the lower centres ; (3) the power 

 to maintain equilibrium ; and (4) the use of the abdomen in swim- 

 ming. 



(c) The sub oesophageal ganglia are the centres for coordinating 

 (1) the locomotive, and (2) the feeding movements, and (3) for a 

 j)eculiar rhythmic swim of the limbs seen as soon as the supra- 

 oesophageal ganglia are removed (the sub oesophageal ganglion is 

 apparently the source of a considerable amount of motor energy). 



(d) There is much less solidarity, a much less perfect consensus, 

 among the nervous centres in the crayiish than in animals higher in 

 the scale. The brainless frog, e. g., is motionless, except when stimu- 

 lated, and even then does nothing to suggest that its members have a 

 life on their own account ; whereas the limbs of a crayfish deprived 

 of its first two ganglia, are almost incessantly jjreening, and when 

 feeding movements are started, the chelate legs rob, and play at 

 cross-purposes with, each other as well as four distinct individuals 

 could do. 



(e) Some stimulus from other centres is more or less necessary to 

 the activity of any given centre, 



(/) The " natural " discharge of a ganglionic centre (not exhibit- 

 ing " volition ") api^ears to be of a rhythmic kind ; the rhythmic 

 movements becoming converted into varied movements by temporary 

 augmentation or inhibition. 



Influence of Heat on the Nervous Centres of the Crayfish.*— 

 M. Richet commences by describing an experiment, by which he says 

 the state of the nervous centres which preside over the power of move- 

 ment may be well tested. If a healthy crayfish is held by the back 

 between two fingers, it attempts to seize objects between the two 

 branches of its pincers, and if the edge of the inner one be lightly 

 touched the two parts are immediately brought together. Regular as 

 this action is, it is not purely reflex, for in the water the crayfish does 

 not act in the same manner; instead of trying to seize its aggressor, 

 the animal may attempt to escape. Of the true reflex acts three are 

 taken as examples. When the antenufe are cut or pinched, the animal 

 withdraws them ; when the eyes are touched, their supporting j^edicels 

 are retracted. Section of one of the large pincers produces swimming 

 movements, to the number of five or six, of the caudal appendage. 



Now in submitting a crayfish to high temperatures, the dilferent 

 functions of the nervous system are seen to disajjpear, one by one, as 

 the temperature is raised : — 



1. '23°-24° : The pincer is most feebly moved ; or the voluntary 

 nervous system is affected. 



2. 24°-26° : No movement of the pincer under the conditions of 

 the experiment above detailed ; or comjslete loss of voluntary nervous 

 activity. 



* 'Comptes Roudus,' Ixxxviii. (1879) p. 977. 



