380 Mr. J. Ward. On the Physiology of the Nervous [Mar. 6, 



the exception of tlie swimmerets and possibly the gnathites. The change 

 is most marked in the antennae and eye- stalks, which barely respond 

 to considerable excitation ; and after these perhaps in the abdomen, 

 the power of swimming or turning over being generally entirely lost. 

 The muscles connecting the abdominal segments on the injured side 

 are relaxed, and the tail-fin appendages on that side are no longer 

 spread out in the normal manner, but remain more or less overlapping 

 and hang down like broken limbs. This leads to a want of symmetry 

 which is most conspicuous during movement : it almost disappears 

 when the nervous connexion with the abdomen is entirely severed by 

 a cut between the first and second segments. No clear difference is 

 discernible in the pinch of the two chelae, but in prehension and 

 locomotion all the limbs on the side of the injury are weakened. In 

 consequence of this, when walking forward the course taken is 

 towards the sound side, in backing the course is towards the injured 

 side. The chelae daring progression show a bias towards the sound 

 side ; that is to say, when the right commissure is cut, they are both 

 directed towards some position on the animal's left, and vice versa 

 when the left commissure is cut. There is a tendency when walking 

 to flop suddenly forwards, and in some cases to "wabble " from side to 

 side. 



II. So long, however, as the other commissure remains intact, there 

 is no lack of spontaneity and purpose in the movements of the cray- 

 fish ; but when this too is severed, that is, when both commissures con- 

 necting the supra- with the sub -oesophageal ganglion are divided, every- 

 thing of the kind disappears, save that occasionally the antennae are 

 waved about in the normal fashion, though much more feebly. The 

 animal lies on its back, the maxillipedes, the chelae, and the first three 

 pair of legs, for the most part, swinging slowly to and fro in perfect 

 tempo ; not, however, as the swimmerets do, both sides synchronously, 

 but with the movements of one side alternating with those of the 

 other. On a very slight disturbance, and at intervals, without any 

 obvious cause, this rhythmic swing gives place to feeding or 11 preen- 

 ing " movements, the last being chiefly confined to the fourth pair of 

 legs, which take no part in the rhythmic swing. The feeding move- 

 ments are a perfect mimicry of the movements made when food is 

 actually seized. These last appear to be in all respects perfectly co- 

 ordinated ; so much so, indeed, that the chelate legs will wait their 

 turn to pass their morsel to the mouth when scraps are placed in all 

 of them at once. But neither they, nor the chelae, nor the posterior 

 maxillipedes, show any selective power, even the animal's own 

 antennae being seized : the first evidence of taste appears when the 

 food gets within the gape of the mandibles. 



When placed on a table, the ambulatory legs are straightened out so 

 as to lift the body as if upon stilts, the half flexed abdomen barely 



