2O2 



HISTOLOGY 



per.' - 



SW. c.-- 



nv. 



A step higher in the relations of a tactile 

 perceptory cell to its intermediate cells is 

 to be seen in the epithelium of the cat's 

 foot or the Guinea pig's skin (Fig. 181). 

 Here the sensory ending comes into contact, 

 by cup-shaped swellings called menisci, with 

 certain of the epithelial cells instead of with 

 any of them. Those so distinguished are 

 called, erroneously perhaps, tactile cells. If 

 they can feel and transmit their sensation 

 as an impulse to the meniscus-bearing cells, 

 then they would be true tactile cells, and 

 the menisci would belong to communica- 

 tory cells. As they are most probably only 

 differentiated slightly to intensify, soften, or 

 otherwise qualify the motion which they 

 mechanically transmit, they are rather to 

 be regarded as slightly specialized interme- 

 diate cells and not of any nervous function 

 whatever. 



We shall now examine a group of tactile 

 organs with highly developed, multicellular, 

 intermediate tissues. These intermediate 

 tissues are constructed so as to transmit 

 the pressure to the nerve-ending on the hy- 

 draulic principle that any pressure, exerted 

 from the outside upon the walls of a closed 

 cavity containing a fluid, will be transmitted 

 to all inner surfaces of the walls and also to the surfaces of any objects 

 contained therein, at a certain ratio per 

 unit of surface. 



The nerve-endings from one or 

 more fibers, in these organs, enter the 

 interior of a closed sac formed by sev- 

 eral coverings of a lamellar connective 

 tissue. Here they lie in a quantity of 

 a fluid or semifluid substance which 

 transmits the pressures that they are 

 intended to perceive. We shall study 

 two examples of this kind of struc- 

 ture tO become acquainted with the FIG. 181. Sensory (tactile) nerve-endings 

 tWO chief Variations. among the stratified epithelial cells of a 



cat's toe. x 600. (After DOGIEL in 



The first of this kind of nerve- Arch.f.mik.Anat.) 



FIG. 180. Tactile nerve-endings 

 in the integument of the earth- 

 worm, nv., nerve; sn.c., sense 

 cells; per., perceptory cell-or- 

 gans projecting through the cuti- 

 cle. (From SCHNEIDER after R. 

 HESSE.) 



