1G8 



COMPARATIVE ANATOMY. 



and to the beak (cere), and lie much more closely together, form- 

 ing definite masses, or "tactile corpuscles." Each of these 

 is surrounded by a nucleated connective-tissue investment, from 

 which septa extend into the interior, partially separating the 

 individual tactile cells from one another. 



FIG. 138. A TACTILE CORPUSCLE (END-BULB) FROM THE CONJUNCTIVA OF A 



MAMMAL. 



N, nerve (the neurilemma of which at t becomes continuous with the investment of 

 the tactile corpuscle ; K, K, nuclei in the investment ; N, the coiled termination 

 of the nerve (axis-fibre) passing to the tactile cells ( T, T). 



t 



Nl 



FIG. 139. A PACINIAN CORPUSCLE FROM THE BEAK OF THE DUCK. 

 (After J. Carriere.) 



ZZ, cells of the nerve-sheath ; L, longitudinal, and Q, circular layers of the in- 

 vesting lamellae ; JX, central knob, with the two pillars of cells ; A, axis-fibre, 

 with protoplasmic investment, entering the corpuscle at A 1 ; MS, medullary 

 sheath ; Nl, neurilemma, which becomes continuous with the investment of the 

 corpuscle at f, f. 



In Mammals the tactile cells are either isolated, as, for instance, 

 on the hairless portions of the body, or they give rise to oval corpus- 

 cles, each consisting of a many-layered and nucleated investment, 

 into which a nerve passes, becomes twisted up, and ends in one or 

 more terminal ganglion cells (Fig. 138). 



