HUMAN TESTIS AND EPIDIDYMIS 405 



These numbers are not affected to any appreciable extent by the 

 formation of new branches, as in no case have I found more than 

 five or six of these in one Wolffian body. That the tubules must 

 remain as functioning and useful parts of the embryo longer than 

 is suggested by MacCallum will be evident when we consider that 

 the kindey in man is only beginning to be provided with glomeruli 

 and convoluted tubules in an embryo of 20 mm. ; but there seems 

 to be no constant relation between the size of the Wolffian body 

 and the growth of glomeruli in the kidney, since the kidney in 

 pig is fully as far advanced at 20 mm. and in later stages as in 

 man, in spite of the much larger and longer lasting Wolffian body. 

 Hill agrees with Pohlman, that the vascularization of the human 

 kidney takes place between 25 and 30 mm., a little later than the 

 presence of glomeruli would indicate, and gives the size for pig 

 embryos as 28 mm. The cause of the continued growth and activ- 

 ity of the mesonephros in the pig and several other animals, even 

 after the kidney is apparently able to act as an excretory organ, 

 is a subject which I shall have to leave for future investigation. 



Of these mesonephric tubules the 6th to the 20th in pig, the 12th 

 to the 20th in rabbit lie, according to Allen, opposite the rete 

 region, and presumably (though it is not so stated by him) join 

 with the rete cords. In man the rete region is more cephalad, 

 opposite the first eight or nine glomeruli ; but the rete cords anas- 

 tomose not only with these but with many others in their course 

 down the mediastinum. Occasionally the first one or two glom- 

 eruli do not join the rete, and remain as small cysts, losing their 

 tubules (fig. 3). Such isolated glomeruU would give rise to the 

 appendix epididymis, described by Toldt as being present in 27 

 per cent of cases examined. The disconnected tubules of such 

 glomeruli would end blindly, as shown in fig. 3 and 4, and in 

 fig. 12, and would ordinarily lie inconspicuously among the con- 

 volutions of the epididymal duct ; if the upper glomerulus and its 

 tubule were separated by a considerable distance from the others, 

 as I have seen it in two of the embryos studied, this blind tubule 

 might form the infrequent lower paradidymis of Toldt, a single 

 tubule in a connective tissue sheath lying behind the head of the 

 epididymis. 



