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ARTHUR E. GILES. 
which 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 geuital 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 ? (2) 
How does the transition from this condition to that found in 
the adult take place ? 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 ; x 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 8 mm. long, that is, soon after the first appear- 
ance of the external gills, the three primitive openings of the 
pronephros into the body-cavity can be seen. The tubules 
forming the pronephros 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 nu- 
cleolus. 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 
1 ‘Comparative Embryology,’ vol. ii, p. 747. 
