0. G. Farriwjton — The Wephrostomei^ of Raua. 311 



they can l)e traced inward depends on the favorableness of the sec- 

 tion. The one shown in fig. 3 extends inward for a distance of -16""", 

 By tracing the openings onward through successive sections we find 

 them passing into a tube of an average diameter of -06'"™, which con- 

 tinues its course near the ventral surface of the kidney [n. t. fig. 2). 

 The tube finally loses its distinctive structure and opens probably 

 into the capillaries flowing toward the vena cava inferior. This inner 

 termination, however, it was found impossible to trace with certainty, 

 though it was sought for with the greatest care through a large 

 number of sections. The opening at the point of junction is undoubt- 

 edly extremely small, so that the chances of finding a section in 

 which it could be traced with certainty would be few indeed. The 

 nature of the epithelium lining the nephrostome is shown in fig. 3. 

 It is seen to be made up of large cuboidal cells having well defined 

 nuclei and resembling in size and shape the cells of the uriniferous 

 tubiiles, though they lack the striations which usually characterize 

 these. At the opening on the surface the cells become flattened and 

 smaller and the cell outline is less distinct. 



The nephrostomes of tadpoles were found to possess a similar epi- 

 thelium, but in the tadpoles the cells are more nearly like those of 

 the uriniferous tubules than in the adult frog. 



The method of preparation of these kidneys and of those of the 

 frog was to preserve in Miiller's fluid 24 hrs., transfer to 95 per cent, 

 alcohol and stain with hsematoxylin. 



II. The cilia appear so plainly in sections that there can be no 

 doubt of their presence. Further evidence of ciliary action was 

 obtained, however, by adoption of the method proposed by Nuss- 

 baum (1. c), which he describes as follows : " Chloroform the animal 

 until respiration has ceased. Inject in the body cavity 0*5 pei" cent, 

 salt solution containing powdered carmine. Close the body Avail. 

 Immerse the animal for 3 hrs. in Muller's fluid and after 12-24 hrs. 

 transfer the kidney to alcohol." 



As Nussbaum states, thin sections of the kidney will then show the 

 carmine distributed through the funnels and tubes, thus giving posi- 

 tive evidence that its fine particles have been carried inward by ciliary 

 action. Such a section is shown in fig. 2. Ilaslam states (1. c.) that 

 having placed properly dissected frogs in 0*6 per cent, sodium chloride 

 solution in which finely divided gamboge was susi)ended, no trace 

 of ciliary action was in any case found on either surface of the 

 kidney. In what way it was anticipated that the ciliary action 

 would show itself is not stated, but it is doubtful if the cilia of 



