Mr Gulland on the Sense of Touch in Asfcacus. 179 



dipterous larva among simple set?e one feathered along one 

 side, and this must be developed at the completion of the 

 metamorphosis into the strong setae closely resembling the 

 tactile setse of Astacus, which Leydig ^ has figured in Musca 

 vomitoria. The undoubtedly tactile seta which Claus figures 

 in Sida (see PL VIII., Fig. 9) shows a slight feathering or 

 serration, which in this low crustacean is ]3robably only in 

 process of disappearance. 



Explanation of Plates. 



Plate VIIL 



Fig. 1. Tactile seta from great claw, seen from above. 



Fig. 2. Stunted fringing seta from great claw. 



Fig. 3. Nerve -ending from claw of Astacus. b.c, blood-corpuscle; g.n., 

 nucleus of ganglion-cell; ner. n., nucleus of nerve-fibre; c.t, conn. tiss. 

 trabeculfe ; etc., conn. tiss. corpuscle; end. n,, nucleus of endothelium. 



Fig. 4. Tuft of tactile setse from great claw. 



Fig. 5. Nerve (from claw) dividing to enter three nerve-endings, hy., 

 hypo dermis cells ; N., nerve ; g.n. and ner. n. {see Fig. 3). 



Fig. 6. Olfactory setse from antennule of Thysanopoda, showing feathering 

 on one side ; 0., olfactory seta; T., tactile seta ; a., from the side ; &., olfac- 

 tory seta from the front. 



Fig. 7. Peculiar fringing seta from maxillipede oi Astacus. 



Fig. 8. Tactile seta of Branchijms (after Leydig) to show the nerve-ending. 

 Oz., ganglion-cell ; Maz., matrix (hypodermis) cells ; T., tactile seta. 



Fig. 9. Tactile seta of Sida (after Claus). Gz., Maz. (as above); Af., 

 "axial thread" (Achsenfaden) ; Ma., "extension of the matrix into the 

 seta ;" N., nerve. 



Fig. 10. Tactile seta ol Ptychoptera (after Grobben). 



Plate IX. 



Fig. 11. Tactile setse of Corethra (after Weismann), to show the gradation 

 from the feathered to the unfeathered form. 



Fig. 12. Small tactile setse oi Astacus. a., from a swimmeret ; hy., hj^po- 

 dermis cells; N., nerve; h., from the palp of the mandible, showing serration. 



Fig. 13. Fringing seta from the side of a swimmeret, too long to be figured 

 entire, int., integument ; cl. p., closing plate (seen from the anterior surface). 



Fig. 14. The two distal joints of a thoracic appendage of Thysanopoda. 

 T., tactile seta ; F., fringing seta. 



Fig. 15. Tactile seta from thoracic appendage of Thysanopoda to show- 

 slight feathering. 



Fig. 16. Fringing seta of Thysanopoda, too long to draw in its entirety. 

 ' Fig. 17. Diagram of the course of the nerve {N.) in the paspodite and 

 dactylopodite of 4th thoracic appendage of Astacus, and of the position of 

 the tactile tufts {T.t.). G., ganglion. The muscles are coloured pink. 



Fig. 18. Short and stout tactile seta from 1st maxilla oi Astacus. 

 1 Zur Anatomic der Insecten, Taf IV., Fig. 36. 



