DISTRIBUTION OF NON-MEDULLATED NERVE-FIBRES. 27 



the capillary blood-vessels, we find that the nerves of the third 

 order form a perivascular plexus, out of which there proceeds 

 a network of filaments of the fourth order, which belongs to 

 the wall of the vessel. 



The relation of the finer nerves to the glands of the skin 

 of the frog has lately assumed greater importance since En- 

 gelmann (32) has demonstrated that the gland-cells are con- 

 tractile, and that this contractility is of essential importance 

 for secretion. The glands of the nictitating membrane are 

 analogous to those found on the web and other parts of the 

 skin ; what, therefore, we affirm regarding the nerves of the 

 former we may regard as applying to the glands of the skin 

 in general. Our investigation refers, however, only to the 

 relation of the nerves to the body of the gland ; regarding the 

 duct, we have here nothing to say. 



As in capillaries, we see in the case of the glands nerve- 

 fibres of the third order, leaving with a tortuous course the 

 nerves which are still furnished with a nucleated sheath, and 

 belong to the second order. In the immediate circum- 

 ference of the body of the gland they unite by lateral 

 branches to form a plexus which envelopes it. (We have 

 remarked above that these nerve-fibres represent small 

 bundles of fibrils, so that at the union of two nerve-fibres 

 there does not result a reticulate, but a plexiform union of 

 the fibrils.) 



The filaments of the fourth order proceeding from this 

 plexus, pursue their course through the membrana propria of 

 the gland (which is furnished with oblong nuclei), and then 

 run between the gland-cells. 



If we carefully direct our attention, at a spot where the 

 gold-colouring is not very intense, to the wall of the gland- 

 body seen in profile (the preparation is arranged with the 

 bottom of the gland looking upwards), we see the following 

 appearances. External to the gland-cells, which consist of an 

 imiformly gi-anular protoplasm, possess a nucleus (lying in the 

 outer third of their area, mostly oblong, less often rounded), 

 and are shaped sometimes cubical) y, sometimes cylindrically 

 and conically, there is a thin clear double-contoured 

 wall, in which oblong nuclei appear at regular intervals. 

 If we confine our attention to the body of the gland, in this 

 case to the most superficial plane in which the gland can 

 possibly be seen, we observe branched structures, which are 

 coloured somewhat more deeply than the gland-cells, pene- 

 trate by their processes between the gland-cells, and seem to 

 blend with the intercellular cement of the same : in these 

 structures there is sometimes to be observed an oblong 



