Mr Gulland on the Sense of Toitch in Astacus. 153 



joint, one much larger than the rest; and he figures the 

 approach of the nerve to it with a very low power. 



Lemoine ^ was the first to investigate the subject from a 

 physiological standpoint. By the use of forceps, percussion, 

 needles, and stimulation by electricity, he finds that certain 

 parts are more sensitive than others (to these I shall refer 

 in the course of this paper), but only in the case of the 

 antennae, antennules, and the " limbs " has he supplemented 

 these observations by microscopic examination ; and here he 

 finds setae " straight, cylindrical, tapering at their extremity," 

 which he associates somewhat tentatively with the sense of 

 touch, and which, though he does not figure them, must, 

 from his description of their structure and position, be 

 identical with the setae which I recognise as tactile. 



Braun2 describes incidentally two kinds of set^ in the cray- 

 fish, identical with those which I recognise, and gives their dis- 

 tribution in a general way; but any consideration of their physi- 

 ology is foreign to his purpose, and he does not enter into it. 



Glaus ^ recognises that the feathered setae, " Fiederborsten," 

 are merely rowing organs — " Euderborsten " — but says that 

 the short and simple spines are touch-organs, and possess an 

 " axial-thread " in their striated contents ; to them runs a 

 nerve, which is provided with a ganglion-cell, and, passing 

 between the matrix-cells, becomes continuous with the axial- 

 thread (" Achsenfaden "). He does not figure this arrange- 

 ment with a high power in any of the Argulids, but gives a 

 drawing representing a similar arrangement in Sicla, which I 

 reproduce (PL VIII., Fig. 9). 



I cannot accept the view of the nerve termination which 

 regards it as running quite to the end of the seta, for not 

 only do my own positive observations, as well as those of 

 Hensen and others, directly contradict it, but the whole 

 history of the formation of the setae and the phenomena at 

 the moult, as given by Hensen and Braun, go to prove its 



1 Rech. pour servir a I'histoire des systemes nerveux, musculaire, et glandu- 

 laire de I'Ecrevisse, Ann. des Sciences Naturelles, Serie 5, tome ix., 1868. 



2 Ueber die histologischen Yorgange bei der Hautung von Astacus fluviatilis, 

 Arbeiten aiis dem Zoologischen Institut zu "Wiirzburg, ii., 1875. 



^ Entwicklung, organisation und systematische Stellung der Arguliden, 

 Zeit. f. wiss. Zool., 1875, pp. 240, 241. 



