GLANDS. 125 



In the human testis the same process has been demon- 

 strated. 



The testicle is developed from the internal sub- 

 stance of the Wolffian body, whilst its excretory duct 

 is formed by the external canal of the same organ 

 The vas aberrant takes its origin from the centre of 

 the Wolffian body, from which, according to some 

 authorities, the epidydimis also is formed. The his- 

 tological changes which take place during the deve- 

 lopment of the testicle are not demonstrable with 

 sufficient certainty to justify their formal description. 



What has been said already in reference to the 

 epithelium, and mode of secretion, of glands composed 

 of clusters of follicles, applies with equal force to 

 those composed of tubes. Those which possess a 

 single layer of epithelium, and in which secretion is 

 effected by simple filtration, are : the glands of the 

 intestinal canal, those of the uterus, the sweat glands, 

 the kidneys, and the liver. 



The glands which have a stratified epithelium, and 

 in which secretion is effected by vegetation of its 

 cells, are the ceruminous glands, and the testicles. 



SECT. III. MIXED GLANDS. The ovary in some 

 respects resembles the blood-glands, but differs from 

 them by possessing an excretory canal, and by the 

 peculiar character of its follicles ; the liver, with its 

 double apparatus for the secretion of bile and sugar, 

 is both a tubular and a blood-gland. The structure 

 of these two organs makes it necessary, therefore, to 

 associate them together in a separate group, which 

 constitutes naturally a connecting link between the 

 true and blood-glands. 



