TERMINATIONS OP NEEVES IN TORTOISE-SHELL. 567 



In fig. 4 a very small portion at the outer part of a sensi- 

 tive spot is more highly amplified. At the upper part of the 

 figure the epithelium outside the spot is seen. Below this the 

 terminations of the nerves can readily be made out. They 

 certainly pass into the nuclear cavity. Whether they end in 

 little flat plates within the nuclear cavity and closely applied 

 to the outside of the nucleus^ or whether they are prolonged 

 into the chromatin of the nucleus, I should not like dog- 

 matically to state. I am inclined to believe in the latter view, 

 and think it probable that they are continued into true nuclear 

 substance. The appearances seen at e e e, fig. 4, are pro- 

 bably due to shrinkage as a result of treatment with alcohol ; 

 but in c c, fig. 4), the nuclear cavity is completely filled by the 

 nucleus, all the chromatin substance having apparently gone 

 to form the knob or cup at the end of the nerve, leaving the 

 rest of the nucleus almost devoid of granular matter, and very 

 faintly tinted by the hsematoxylin. 



The nerves end in the cells of the rete alone, for it is impossi- 

 ble to trace them beyond the deeper layer of the epithelium. 

 This is what might be expected, for in the adult tortoise-shell 

 the rete consists of one, two, or perhaps three layers of nucle- 

 ated rounded cells, and above these, with hardly any transi- 

 tional tissue, there are the dense laminae of the horny layer, 

 made up of flattened keratinised scales with unstainable nuclei. 



It follows from the foregoing remarks that the scutes of the 

 tortoise, in spite of their hard, dense nature, form a very typical 

 epidermic sensory covering for the animal. As in the soft 

 skin of mammals, the nerves end in localised sensitive spots 

 in the epidermis, and before penetrating this tissue they form 

 a horizontal plexus in the upper part of the connective tissue. 



The final terminations of nerves in epithelium has received 

 much attention from histologists, who have studied this sub- 

 ject perhaps most fully in the tadpole's tail. 



In some situations the nerves appear to run entirely between 

 the cells — indeed, this appears to be generally the case (Ran- 

 vier, 1; Klein, 2 ; Eberth, 3; Leboucq, 4). They either end in a 

 simple plexus, or terminate in very small knobs or plates, which, 



