Bennet Mills Allen 



91 



The material Avas, in practically all cases, fixed in Flemming's fluid 

 and stained with Heidenhain's iron hematoxylin with a counter stain 

 of Siiurefuchsin, Orange G. or Bordeaux red. Sections were cut to a 

 thickness of 6f /j or in a few cases 10 /u and were mounted in series. 

 It was, of course, necessary in all cases to section the anterior part of 

 the mesonephros together with the sex gland itself. 



An account of the earlier literature upon this subject would be use- 

 less repetition, since we have such valuable and extensive reviews as 

 those given by Waldeyer, 70 and 02, Born, 94, Coert, 98, Winiwarter, 

 00, Bouin, 00, Mihalkovics, 85. In the general summary reference 

 will be made to some of the more recent and important works bear- 

 ing upon these problems; but no attempt will be made to attain com- 

 pleteness in a consideration of the earlier literature, a very large part 

 of which is of merely historical value. 



II. GENERAL TOPOGRAPHY. 



The orientation of the various organs to be considered may be well 

 understood from, a study of the pig embryo of 2.5 cm. length (Text 

 Fig. 1 and Plate I, Fig. 1). The 

 mesonephra are a pair of elongated 

 laterally compressed bodies attached to 

 the dorsal body wall on each side of the 

 mesenter}'. Their long axes diverge 

 anteriorly and converge posteriorly. 

 They are prominent structures, extend- 

 ing three-fourths of the length of the 

 abdominal cavity, being closely united 

 to the dorso-median part of its wall by 

 their short, broad mesenteries. Each 

 mesonephros is flattened on its median 

 face while the lateral face is convex. 

 A sharp ridge extending the entire 

 length of the medio-ventral face marks 

 the course of the Wolffian and Miil- 

 lerian ducts, the latter being ventral to 

 the former. The genital ridge is situ- 

 ated on the median surface of the mesonephros and extends its entire 

 length immediately ventral to the mesentery. It is covered by a thick- 

 ened layer of epithelium continuous with the general peritoneal lining 

 of the abdominal cavity, yet differing from it in that its component 

 cells are columnar instead of fiattened, and are closely crowded together, 



Fig. ]. Mesonephros and associated 

 structures. Pig embryo of 3.5 cm. length. 

 a. r., adrenal body ; e. p., epithelial plate ; 

 m. r., mesenteric ridge ; r. c, rete ridge ; 

 t., testis ; W. M., WoliBan and Mullerlan 

 ducts. 



