188 JOHN LEWIS BREMER 



steadily to 32.0 mm., while in the guinea pig and in man signs 

 of involution soon set in, and bj^ 15.0 mm. in the guinea pig the 

 organ can no longer be considered active. In man the state- 

 ments of many investigators are so conflicting as to the time 

 of this involution that it is impossible to draw any very definite 

 conclusions, but from my own observations it seems that the 

 Wolffian body may be functional later than has been usually 

 supposed, though many of its glomeruli certainly degenerate 

 early. 



In order to have some definite ideas as to the relative length 

 of time during which the Wolffian body, or at least that part 

 of it represented by the glomeruli, may be considered functional 

 in the different kinds of mammals studied, 1 have counted 

 and measured the active glomeruli in different ages of embryos. 

 This can give at best but crude, inaccurate results, since the 

 diameter of a glomerulus may have no definite relation to the 

 area of its surface and to the area of the epithelial plates on 

 that surface; the diameter tells us nothing of the amount of 

 lobulation, each new lobule increasing the surface area, nor of 

 the ratio of epithelial plates to the protoplasmic bodies of the 

 epithelial cells. Still the inaccurate results are sufficiently 

 striking for the purpose of showing the great variation which 

 exists between the different types of animals. 



At one end of the scale are the embryos of the mouse and rat, 

 which never develop mesonephric glomeruli. Next to these 

 come the embryos of the guinea pig, in which the glomeruli 

 are immature at 8.0 mm., are never large or numerous, and 

 have undergone marked degeneration at 15.0 mm., when there 

 are only fourteen in one Wolffian body, with an average diame- 

 ter of about 52 micra. Even these few small glomeruli could 

 hardly have been properly functional, as they lack almost en- 

 tirely the epithelial plates. The mole, according to Weber and 

 others, is in the same class as the guinea pig, with few, short- 

 lasting glomeruli. In the rabbit there is early a large organ; 

 an embryo of 9.6 mm. has about forty active glomeruli on each 

 side, with an average diameter of 110 micra. This increases 

 only to forty-two glomeruli in an embryo of 14.5 mm., as many 



