324 



EPITHELIAL AND ENDOTHELIAL TISSUE. 



with chloride of gold, can be recognized by their beaded appearance and their 

 dark violet color run in the cement-substance between the epithelia, and in 

 this situation are in direct union with the filaments ("thorns") interconnect- 

 ing the bioplasson reticulum of neighboring epithelia. (See Fig. 140.) In 



JLC 



FIG. 140. DIAGRAM OF TERMINATION OF NERVES IN EPITHELIAL LAYERS. 



AC, axis-cylinder, dividing into axis-fibrillas, AF, which penetrate the hyaline or base- 

 ment membrane, H, and course in the cement-substance between the columnar epithelia, 

 CO, and the cuboidal epithelia, CU. The axis-fibrillse are directly connected with the trans- 

 verse filaments in the cement-substance, and indirectly with the bioplasson reticulum of the 

 epithelia. 



this way, the active portion of the epithelia the living matter is controlled 

 by the nerves. Here and there a beaded thread can be traced into the body 

 of an epithelium, and this occurrence is easily understood if we bear in mind 

 that the nerve-fibrillae and the reticulum of living matter are, in essential 

 points, identical formations. The only reliable means for tracing the nerve 

 terminations is by chloride of gold staining. It is absolutely necessary, how- 

 ever, first to find the connection of the axis-fibrillas with larger medullated 

 or non-medullated nerves before we can positively determine their nervous 

 nature. 



Recently, a number of formations in the organs of sense have been termed 

 Neuro-epithelia (Schwalbe). This refers to formations which are either epi- 

 thelia or take a genetic origin from epithelia, and represent the terminations 

 of the sensual nerves. In this group are included the rods and cones in the 

 retina of the eye, which are composed of a number of transverse disks ; the 

 outer portions of the rods during life show a bright red color, which, by its 

 discoverer, Boll, was termed the " visual purple." The rod- and cone-fibers, 

 with their nucleated nodules, constitute the external granular layer of the 

 retina. In the labyrinth, or the internal ear, especially in the maculae and 



