296 BULLETIN OF THE 



volved, for example, in the accouut — coutested, it is true — given by 

 Carius ('88) of the anterior growth of the chorda in the " Kopftbrtsatz " 

 of Cavia, the chorda being in intimate fusion with the underlying ento- 

 derm ; or, again, the backward growth of the Amniotic Miillerian duct in 

 close connection both with the Wolffian duct and with the adjacent peri- 

 toneum, as descriljed by a number of recent writers. 



In conclusion, then, I am of opinion that the more primitive condition, 

 and that shown by most Vertebrates, is the development of the segmen- 

 tal duct independent of connection with the ectoderm ; but that in cer- 

 tain groups the duct enters into a secondary union with the ectoderm. 

 The question whether the ectoderm here contributes material to the 

 fundament of the duct can at present receive no more definite answer 

 than that contained in the foregoing discussion. 



It has frequently been asserted that the mesodermal origin of the kid- 

 neys is not in harmony with our conceptions of the derivatives of this 

 germ layer. As early as 1855 Remak saw a fundamental opposition in 

 the mode of development which he described for the excretory organs, 

 and that familiar in the case of other glands. According to his view, 

 which received very general acceptance, the kidney is a unique example 

 of a gland w'hose secreting surfaces are not derived from one or other of 

 the bounding germ layers, ectoderm and entoderm. 



In my opinion, this view must now be considered inaccurate. It is 

 doubtless true that glands are usually developed either from the ecto- 

 derm or from the entoderm ; this circumstance may merely be due to 

 their apparently being seldom needed on mesodermal surfaces. Certain 

 special regions, however, seem to require glands. Such regions are the 

 sexual conduits in which, besides those glands which have special func- 

 tions, such as the deposition of the secondary egg membranes ^ (Ludwig), 

 we should expect to find glands similar to those which are found in the 

 course of other canals leading to the exterior, such, e. g., as the trachea. I 

 shall disregard the glands which develop in the ampullte of the vasa defer- 

 entia, since these are derived from the Wolffian duct and consequently may 

 be of ectodermal origin in Mammals, and shall take as a specific example 

 the genital tract of the human female. It seems very certain that in Am- 

 niotes the Miillerian duct develops entirely independently of the Wolffian 

 duct, as an evagination of the peritoneal covering of the Wolffian body. 

 Moreover, whether we accept the view of van Ackeren ('89), that the 

 hymen marks the region of fusion between the fused Miillerian ducts and 



1 The albumen secretion of the Hen's oviduct is a familiar example. According 

 to Giacosa (72) the oviducal secretion in Rana is largely composed of mucin. 



