The determination of sex in animal development. 733 



ripening. The topography of the reproductive organs in the common 

 leech points in a like direction ^). 



Unless the procedure have been modified in some such way as 

 just indicated in order to meet special needs, the final division, prior 

 to ripening, has every appearance of being the turning-point of sex- 

 differentiation. There is, so it would seem, a very close and significant 

 connection between the determination of sex and the phenomena of 

 the reduction. The one follows naturally upon the other. A germ- 

 cell, which has had the stamp of sex placed upon it; that is to say, 

 one whose destination has been decided in a certain direction, must 

 of necessity go through the procedure of formation of gametes — 

 entailing the phenomena of reduction — before it can fulfil its assigned 

 office. Looked at in this light the following words of Rückekt ac- 

 quire a special significance: "It (the reduction of chromosomes) is 

 initiated before the ripening, perhaps already in the oö- and spermato- 

 gonia, by the omission of a transverse division of the chromatin- 

 coil, as a result of which each two chromosomes remain linked to- 

 gether" (in: Ergebn. Anat. Entw., V. 3, 1894, p. 582). 



The above had been written before Meves' recent paper ^) was 



1) In connection with this question section VIII of the present 

 writing should, however, be considered. In this portion of the text 

 the writer has acted largely upon the assumption, that everything in 

 the development must be effected by cell-division. Without question 

 the separation of two categories of unlike gametes must originally have 

 been carried out by mitosis. But after such separation there is nothing 

 to prevent the postponement of the revelation to later periods by the 

 acquirement of the faculty of going through further mitoses. As will 

 appear anon, it is concluded, that the reduction is the outward mani- 

 festation of the determination of sex. Granted the possibility of the 

 separation along two lines some time prior to the reduction and mani- 

 festation of sex, of such a kind, that all the cells produced along either 

 line will have a certain fixed sexual destination, such as would appear 

 to obtain in the leech and Styelopsis, the determination of sex would 

 consist of, or be divisible into, two periods, one of separation by cell- 

 division, the other of manifestation by the reduction. My final con- 

 clusion, therefore, is, that determination of sex by cell-mitosis is rather 

 a theoretical postulate, than an actual fact, although originally it may 

 have been so effected. Actually, it is brought about without mitosis, 

 but it either succeeds a certain mitosis, or, what is the same thing, a 

 certain number of such. 



2) MiovEs, F., Ueber den von v. la Valette St. Geokoe ent- 

 deckten Nebenkern (Mitochondrienkörper) der Samenzellen, in : Arch, 

 mikrosk. Anat., V. 56, 1900, p. 553—606, 2 pl., 1. c, p. 555. 



48* 



