124 ARTHUR E. GILES. 



characterises them later on, and having in this case a peculiar 

 resemblance to the fingers of a hand, as represented in the right half 

 of Fig. 2. Thinking that the light-coloured bodies from which 

 they sprang were the genital organs, these were removed with the 

 surrounding parts, and cut horizontally in successive sections. It 

 was then found that what had been taken macroscopically for 

 genital organs (the real genital organs not appearing so plainly as in 

 Fig. 1) showed microscopically most typical kidney structure, whilst 

 at the same time it was quite continuous with the fat-body at the 

 anterior end. 



Two questions naturally arise : (1) How come the fat-bodies to be 

 in relation with the anterior end of the kidneys 1 (2) How does the 

 transition from this condition to that found in the adult take place 1 

 These questions I propose to answer in the following account. 



Up to the age with which we are concerned, the generative 

 cells are found in the condition of primordial ova, as described by 

 Balfour ;* hence there is no differentiation into ovary and testis. 

 I shall therefore uniformly use the neutral term " genital organ." 



The method adopted was to begin with very young tadpoles, and 

 cut series of sections at various stages and in various planes, with 

 the following results. 



In a tadpole 8mm. long, that is, soon after the first appearance of 

 the external gills, the three primitive openings of the pronephros 

 into the body cavity can be seen. The tubules forming the pro- 

 nephros are actually of larger diameter than they are somewhat 

 later. One of them is represented in Fig. 3, in which it is seen 

 that the cells lining the tubules are cubical or columnar, granular at 

 the part nearest the lumen, and showing a distinct radial striation 

 peripherally. The nucleus is central, and stains readily, as does 

 also the nucleolus. The genital organ at this stage is situated nearer 

 the median line than the pronephros, and anterior to it, and is well 

 defined both anteriorly and posteriorly. 



The young tadpole at the stage we are considering has still a 

 plentiful supply of food-yolk, and is consequently independent of 

 nutrition obtained from without. But now, as it grows, the 

 absorption of the food-yolk proceeds more rapidly, while at the same 



* " Comparative Embryology," vol. ii., p. 747. 



