750 



JOHN BEAED, 



Fig. A. As we have seen, theoretically the determination of sex must 

 in all probability originally be referred to the division of the primary 

 germ -cells into secondary ones. In previous pages this was regarded 

 as the original point. This idea may be reverted to, for the facts 



Fig. A. 



Fiar. B. 



RG.C. 



, -^ Réductions 9'«^. 



■ &0.C I M phases of dekrminaHon 



I 



'(Segg 



Fig. A. Oogenesis and determination of 

 sex in Raja batis, the smooth skate. At 

 P. G. C is shown a primary germ-cell, 

 which by division gives rise to two 

 secondary germ-cells, S. G. C. By the 

 word "Separation" it is indicated, that at 

 this point is the parting of the ways, 

 which will culminate along the one line 

 in -female oocytes, along the other in male 

 ones. The oocytes are labelled O. C. From 

 the separation to the final phases of the 

 determination and reduction there are 

 shown n mitoses along the female line, 

 n + 1 along the male line. The remainder 

 of the figure depicts the "I'ijjeniugs" of a 



and of a female-egg. 



male- 

 Fig. B. For comparison with the 

 j)receding figure there is here shown the 

 probable course of spermatogenesis and 

 determination in Paludina, Pygaera etc. 

 The lettering as before, except H. Sp. C 

 and W. Sp. C, which denote the oocytes 

 destined to form hairlike and wormlike 

 spermatozoa respectively. From the line of 

 kinds of spermatozoa after F. Meves. 



Fig. C. Course of oogenesis and sperm 

 comparison with Figs. A and B 



RG.C. 



Fig. C. 

 _/! _ - -^;-' Oögonia ~-_^ 



/ 



Spermato- oocytes 



Ï- . P gonia 

 ^^Spermatocytes 



tS.G.C. 



9 m 



the reduction to the formation of the two 

 atogenesis in pure hermaphroditism. For 



seen in some hermaphrodite animals, such as the leech and Ascidian, 

 require elucidation. 



It has been pointed out, that the final division of the oogonia 

 into oocytes is the latest period, at which the determination of sex 



