Mr GidloMd on the Se7ise of Touch in Astacus. 171 



In Thysanojjoda, a free-swimming form, there is obviously 

 little need of a complete sensitive investment, and here we 

 find the tactile setce concentrated in the fore-part of the 

 animal, and only present on the tips of the thoracic appen- 

 dages, on the gnathites, and on the two pairs of antennae, 

 which are richly furnished with them ; and which, as they are 

 very long and mobile, compensate the animal (in the same 

 way as in the carapace of Astacus) for the want of tactile 

 setse on the posterior somites. 



In the creeping forms, on the other hand, such as Romarus 

 and Astacus, the necessity for being able to receive tactile 

 impressions from without is evidently much greater, when at 

 any moment danger may threaten these animals from among 

 the rocks and stones where they live; and where, as in 

 Homarus, the integument is so thick and strong that the 

 animal may practically disregard most enemies, the tactile 

 setse are found thickly set at a few points only ; while in 

 Astacus the relative thinness of the integument has brought 

 about a much wider distribution of tactile setse. 



Nervous Apparatus. 



I have studied the nerve-endings, more especially in the 

 " hand " of the great claw, as in that portion of the propodite 

 or 6th joint, which is prolonged to oppose the dactylopodite, 

 there is a mass of connective tissue, which can be drawn out 

 from the hard cuticle and subjected to various methods. 

 That which I found most useful was preliminary treatment 

 with a saturated solution of corrosive sublimate, staining in 

 toto with various dyes, and then embedding in paraf&n, by 

 which means I was enabled to obtain several complete series 

 of sections in various directions. I have also studied fresh 

 sections, and have treated the tissue with osmic acid, chloride 

 of gold, and other re-agents. 



The nerve of the limb divides in the swollen part of the 

 propodite into too large branches, one of which goes to the 

 dactylopodite, the other to the " anvil " of the propodite. 

 These nerves run at the sides of the limb (their course is 

 shown somewhat diagrammatically in PL IX., Fig. 17), giving 

 off branches to the flexor and extensor muscles of the dacty- 



