310 O. C. Farrington — The Nephrostomes of JRana. 



The subject is one of interest, since it is desii-able that we should 

 know at what point in the ascending scale of animal life these organs, 

 which probably exist in all vertebrates as an embryonic feature, cease 

 to characterize the adult forms. 



In the hope that the recent improved methods of section cutting 

 and reconstruction might throw additional light on the question, the 

 work which is described in the following pages has been done by the 

 writer. 



In carrying on this work, all the experiments which were made on 

 the frog were duplicated by similar ones on the newt, and the same 

 is true of all the preparations made for section cutting. This was 

 done in order to compare directly results obtained in a species 

 where the nephrostomes are known to exist, with those given by the 

 frog. 



Two species of Rana were used, Mana Catesbicma and Rana 

 virescens, but no dissimilar results due to difference of species were 

 noted. Of the newt, the species used was the common Dlemyctylus 

 virescens. 



The investigation has led to the following conclusions : 



I. Microscopic sections of the frog's kidney often show, passing 

 inward from the ventral surface, small tubes which are to be regarded 

 as nephrostomes. 



II. These tubes have free, active cilia. 



III. Strong, if not conclusive evidence exists to show that these 

 open into the blood capillaries of the kidney. 



I. Fig. 1 shows a section of the newt's kidney with nephrostomes 

 appearing at various points indicated by the letter n. 



At the surface these have a diameter of about -04'"™, then passing 

 inward show a slight funnel-like enlargement to about -oe™"'. For 

 this part of its course the tube is seen to be made up of a ciliated 

 epithelium, the cells of which are narrow, elongated, somewhat fusi- 

 form, and have indistinct nuclei. Two of these funnels are seen 

 uniting in a common tube, in fig. 1, an arrangement stated by Spengel 

 to be quite common. For the rest of its course the tube, having a 

 diameter of about -024™'", loses its distinctive epithelium and its 

 walls are thin and structureless till it opens into the uriniferous 

 tubule {n. t. fig. 1). Figs. 2, 3 and 4 show sections of the kidney of 

 the frog prepared similarly to those of the newt. As will be seen, 

 these show openings or cavities on the ventral surface, about '035™"' 

 in diameter, lined with a distinctive epithelium and resembling in 

 every respect those just noted in the newt. The distance to which 



