Susanna Phelps Gage 421 



half of the Wolffian ridge, certain of the tubules are directly continuous 

 with the epithelium covering the ridge, but there are no hollow tubules 

 opening into the ccelom. In the caudal half the unsegmented blastema 

 which he considers the fore-runner of the tubules, was not connected with 

 the epithelium. From the description, this is probably a less advanced 

 specimen than No. 148.°'* 



Janosik " found in an embryo, 3 mm. long when fresh, that in the 

 cephalic part of the Wolffian ridge there are a Wolffian duct and a number 

 of independent tubules; the concentrated blastema serially following the 

 tubules, is not segmented, but connects with the coelomic epithelium at 

 intervals. 



MacCallum,'' the latest special investigator on the subject, shows in a 

 3.0 mm. embrj^o (164 of the Mall collection) that extending from the 

 10th to the 19th or last formed myotome there are thirteen enlargements 

 of the Wolffian duct, the 5th to the 8th being considerably elongated, but 

 showing no glomoruli or Bowman's capsules. In No. 80 of the same 

 collection (4.5 to 5 mm. long), there are 17 to 18 tubules with the char- 

 acteristic S-shaped curve, enlarged Bowman's capsule, and union with the 

 Wolffian duet. He showed in this case a close connection of the Wolffian 

 duct at intervals with the coelomic epithelium. In none of these did the 

 tubules open to the coelom. 



It has been my privilege to look over the two specimens described by 

 MacCallum and also a more recent specimen of the same collection 

 (No. 209). These with No. 148 form a series which may throw light on 

 the true development. The following apparently consecutive history is 

 drawn from a study of these embryos ranging from the 17th to about the 

 23d day (see above, Age of Specimen), and from comparison with various 

 embryos of the Cornell University collection as cat, shark, lamprey, etc. 



In the mesonephric region of the least developed stage (No. 164), in 

 respect to the nephric region, the Wolffian duct lying at the dorso-lateral 

 part of the Wolffian ridge has enlargements, some of them, the 5th to the 

 7th, quite pronouncedly thorn-like. In the next stage (No. 209) in which 

 the sections were thick and details difficult to determine there exists a 

 series of about fourteen rounded tubules with thickened epithelial walls, 

 and a lumen well-defined or in process of formation. In the ventral 

 most prominent part of the Wolffian ridge some of these, as the 5th, are 

 connected by a solid out-growth with the coelomic epithelium of the most 



■-■''a Meyer's specimen was 2 mm. long after being hardened, thus making the 

 discrepancy in length less apparent than would be indicated from the 

 measurement 4.25 mm., taken while fresh. 



