341 



considered in connection with an account of the development of the 

 sex-glands of the mammals^). The subsequent work along this line 

 has emphasized more and more the necessity for the exercise of great 

 caution in the interpretation of such apparent transition forms. 

 A section containing only a portion of a given cell may give a very 

 erroneous idea of the cell as a whole. This fact necessitates the 

 exercise of especial caution in the consideration of types of cells 

 whose only recognizable ditferences consist of relative size and yolk 

 content — the characters considered by Bourn in distinguishing the 

 sex-cells from the neighboring peritoneal and mesenchymal cells of 

 R. temporaria. 



NUSSBAUM '80 2) considered the sex-cells to be merely those which 

 have retained their embryonic characters long after the other cells of 

 the embryo have begun to difterentiate. He is very positive in his 

 claim that all of the sex-cells found in later stages of development 

 arise from those first recognizable as such, in contradiction to the 

 view later held by Bouin, who claimed that sex-cells arise not only 

 as above outlined during early stages, but that they continue to arise 

 by transformation of peritoneal cells during later stages as well. His 

 paper, based upon the study of a wide range of stages in the develop- 

 ment of R. fusca and R. esculenta and of the trout as well, should 

 certainly have due weight so far as it goes, although the earliest 

 stage considered by him is apparently one very soon after the sex- 

 cells have moved laterally to their final positions in the anlagen of 

 the sex-glands, "schon früh, wenn die äußeren Kiemen noch bestehen". 

 The stages considered in this paper are of course all earlier than this. 

 While the technique in vogue at the time when his paper was written 

 fell short of more modern methods, in many regards it had certain 

 points of advantage which have been lost by a more general use of 

 the microtome and the cutting of thinner sections. 



The material for the preparation of this paper consisted in a 

 number of tadpoles of R. pipiens ranging from 6 mm. to 8.3 mm. in 

 total length, measured from the tip of the head to the tip of the tail. 

 They were fixed in Tellyesniczky's and Zenker's fluids, and cut in 

 transverse sections of 10 in thickness. This work was finished by the 

 last of April of this year, but its publication was delayed a few 



1) B. M. Allen, '04, The Embryonic Development of the Ovary 

 and Testis of the Mammals. American Journ. of Anat., Vol. 3. 



2) M. NussBAUM, '80, Zur Differenzierung des Geschlechts im Tier- 

 reich. Archiv f. mikrosk. xlnat, Bd. 18. 



