THE SEXUAL ORGANS. 241 



subsequently, include the urethra which is formed by the closure 

 of a groove on its inferior surface. 



With respect to the histological development of these parts 

 little is known. The testes are constituted originally of a 

 uniform cellular substance, which, however, soon begins to 

 divide into transverse rows, forming the rudiments of the seminal 

 tubes. These are, at first, straight csecal canals, extending from 

 the outer border of the testis to the interior, which most pro- 

 bably originate as solid tracts of cells, and only subsequently 

 acquire a cavity and membrana propria. From the continued 

 growth, especially in length, of these primary channels, and 

 the production of offsets from them, the later, convoluted and 

 very long seminal tubes arise ; it appearing, in fact, that an 

 entire lobule of the testis is formed from each of them. The 

 tunica albuginea of the testis and its internal prolongations 

 arise from the primary blastema of the gland, and make their 

 appearance at the same time with the seminal tubes. 



With regard to the physiological relations of the male sexual 

 organs, in the adult, I would here notice the following points. 

 The secretion of semen, in animals, does not go on continuously, 

 like that of the urine, but is intermittent, taking place only at 

 the time of rutting or heat. In Man, the capability of producing 

 semen, assuredly, always exists, although it does not appear 

 to me to follow from this, that semen is being continually 

 formed, and that what is not emitted undergoes absorption ; and 

 consequently it seems justifiable to suppose that the seminal 

 tubes secrete semen only when the secretion has been partially 

 evacuated externally, either in consequence of sexual congress, 

 or of seminal emissions, and an excitement of the nervous 

 system has caused an increased flow of blood to the testis. 

 There are no certain facts in favour of an absorption of the 

 semen when formed, which could only take place in the vasa de- 

 ferentia and vesiculce seminales; for what is observed in animals, 

 after the rutting season is over, has no reference to this point ; 

 and the very circumstance, that in the situations above men- 

 tioned, no traces of a disintegration of the semen are ever found, 

 appears to be very much opposed to such a supposition. At 

 the same time, however, it is perhaps unquestionable, that with- 

 out seminal evacuations, a formation of semen may be possible ; 

 for it is sufficiently established, that a rich, heating diet, and an 



ii. 16 



