GLANDS. 475 



TESTIS. 



The testis, the last of the tubular glands in the human 

 subject, agrees more closely in structure with the sudoriferous 

 and ceruminous glands than with the kidney ; there being this 

 in common between the three first- mentioned, viz., that the 

 tubes, of which they are principally constituted, are convo- 

 luted, and are not enclosed in a dense framework of fibro- 

 elastic tissue, as is the case with those of the kidney. 



The testis is invested by a tunic of white fibrous tissue ; 

 this sends down, into the substance of the gland, nume- 

 rous dissepiments, which divide the tubes of which it is 

 composed into parcels, each of which may be called a lobe. 



The tubes of the testes are remarkable for their large size, 

 great tortuosity, and exceeding and ready extensibility. 

 (See Plate LX. figs. 1. 4.) 



When viewed as opaque objects, the tubes appear of a 

 delicate and semi-transparent whiteness ; and, when seen by 

 transmitted light, they are almost black ; this arises from 

 the fact of the interception of the luminous rays by the cells 

 contained within the tubes. 



The membrane of the tubes is totally distinct from that of 

 most other tubular glands ; it is very thick and fibrous, being 

 constituted of a well-marked form of nucleated fibro-elastic 

 tissue. (See Plate LX.y^. 4.) 



The constitution of the tubes of elastic tissue explains satis- 

 factorily their ready extensibility and variable diameter ; 

 this variation, in specimens prepared for microscopic examin- 

 ation, is very obvious, and arises from the displacement of 

 contained cells, occasioned by unequal external pressure ; 

 where these cells are accumulated in the greatest number, 

 there the tubes are thickest ; and where there are but few 

 cells, or even where the tubes are destitute of cells, they are 

 thinnqst, and frequently even entirely collapsed. 



These facts show that the tubes are highly expansive ; and 

 there is no doubt that their diameter varies, during life, in 

 accordance with the amount of seminal fluid contained within 



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