Mr Gulland on the Sense of Touch in Astacus. 173 



The nuclei themselves are large, ovoid, granular, and contain 

 one or more nucleoli, which refract light very strongly, and 

 usually lie at the periphery of the nucleus (it is possible that 

 they do so always, and that their occasional apparently 

 central position is merely due to the fact of their being seen 

 on the top of or through the nucleus). At the proximal end 

 of the tactile organ, the nerve-fibrils break up and become 

 continuous with tlie protoplasm in the way that has been so 

 frequently described and figured in connection with ganglion- 

 cells, and at the distal end the process is reversed, and the 

 nerve-fibre is re-formed, and is of about the same size, and 

 has the same structure as when it entered the end-organ. 

 It then bends round and passes through the hypodermis in a 

 direction approximately at a right angle to its surface ; in 

 the last part of its course it comes into contact with an in- 

 growth of the hypodermis cells, which is probably the "hair- 

 tube " of Hensen and Braun. 



From a careful comparison of the position of the tufts of 

 setae on the outside of the claw and the nerve-endings within, 

 and from an examination of decalcified preparations, I have 

 come to the conclusion that there are generally three or four 

 nerve-end organs to each of the larger tufts of setae ; at any 

 rate, if the tuft does not consist of more than half a dozen 

 setse or so, one end-organ seems to suffice. Q'he way in 

 which the nerve is connected with the setae is the same in 

 both cases. This concentration is curious, and seems to run 

 parallel with the collection of the setae into tufts. Each 

 nerve-fibre, after leaving the end-organ, and passing after a 

 shorter or longer course through the hypodermis, divides into 

 several branches, one for each seta which it supplies, and 

 these enter the canals which traverse the integument, and 

 whose presence has been demonstrated by Vitzow and others, 

 and which I shall for convenience call " nerve-canals." The 

 hypodermis does not enter these canals, which are only large 

 enough to admit the nerve-fibre. The nerve-filaments run 

 on to the slight dilatation of the canal which underlies the 

 " areola " of the seta ; here they seem to swell slightly, and 

 then they enter the lumen of the seta, which is in direct 

 communication with the lumen of the canal. The nerve- 



