2G SECKETIXG STRUCTURES. 



according to certain laws, and then, after a longer or shorter 

 period, dissolves and disappears in the inter-cellnlar space in 

 which it is situated, its materials passing into the circulating 

 system, if it be an internal, and being merely thrown off if 

 it be an external cell. The primary secreting cell, again, after 

 distention with its secretion, does not change its form so much 

 as certain of the formative cells, but the subsequent stages are 

 identical with those of the latter. It bursts or dissolves, and 

 throws out its contents either into ducts or gland cavities, both 

 of which, as I shall afterwards show, are inter-cellular spaces, 

 or from the free surface of the body. 



The general fact of every secretion being formed within cells, 

 explains a difficulty which has hitherto puzzled physiologists, viz., 

 why a secretion should only be poured out on the free surface of 

 a gland-duct or secreting membrane. 



" Why," says Professor Miiller, " does not the mucus collect 

 as readily between the coats of the intestine as exude from the 

 inner surface ? Why does not the bile permeate the walls of the 

 biliary ducts, and escape on the surface of the liver, as readily as 

 it forces its way outwards in the course of the ducts ? Why does 

 the semen collect on the inner surface only of the tubuli semeni- 

 feri, and not on their exterior, in their interstices ? The elimi- 

 nation of the secreted fluid on one side only of the secreting 

 membrane, viz., on the interior of the canals, is one of the 

 greatest enigmas in physiology." Miiller proceeds to explain this 

 enigma by certain hypotheses ; but the difficulty disappears, the 

 mystery is removed, when we know that the secretion only exists 

 in the interior of the ripe cells of the free surface of the ducts or 

 membrane, and is poured out or eliminated simply by the burst- 

 ing and solution of these superficial cells. 



I have hitherto confined my observations to the structure 

 and function of the ultimate secreting element, the primary 

 secreting cell. I now proceed to state the laws which I have 

 observed to regulate the original formation, the developement, 

 and the disappearance of the primary organ. This subject 

 neccessarily involves the description of the various minute ar- 

 rangements of glands and other secreting structures. 



If the testicle of Syurttux coniubicm (Gmelin) be examined 



