752 JOHN MKAKI), 



case in the skate, two sorts of spermatozoa may not be fully difleren- 

 tiated, the i)r()cediire of forming these must of necessity invariably be 

 initiated. But, as in some instances of oo«;enesis, such as in partheno- 

 •^enesis with complete suppression of the males, it may be arrested at 

 any i)oint after the sepaiation '). This will simi)ly nu;an, that the 

 cell or cells, set ai)art to form a second kind of male ganuîle or sper- 

 matozoon, will undergo degeneration at some i)oint or other i)rior to 

 the (lillcrenliation of gnmetes. This may hai)i)en somewhat after the 

 manner already described for (^icada (Wilcox), or the degeneration 

 may take i)lace at still earlier ])eriods. 



It is concluded, that llie beginning of the determination of sex 

 takes place in the division of the priuuiry germ-cells into secondary 

 ones by a separation along two lines, as shown in the diagrannnatic 

 figuie (Fig. A), and that the iinal step in the procedure, the actual 

 determination of sex, is taken by the reduction of the chromosomes 

 in the oocytes and s])erniatocytes. 



The peculiar phenomena, associated with tiu» reduction, witli the 

 lirst aj)i)earai)ce of tiie diminished number of chromosomes, become 

 intelligible from the above. Allhough, according to the testimony of 

 liovKiM and others, the reduction be not brought to pass by a mitotic 

 division, it ha,i)i)ens in the closing phases of one such, where the 

 oogonia, for example, become oocytes ■"). In its origin the determinati(m 

 of sex nuist have been brought about in the course of some cell- 

 division ; but now, owing to the intercalation of new mitoses, it follows 

 a certain one, and in such a way as to appear to be a part of it''). 



1) This exphiius how the occasional neglect to suppress one or more 

 ol' the forerunners of niale-egf^s in certain cases of parthenogenesis with 

 tlie usual absence ol" nuilo individuals but v^ith their rare and sporadic 

 a})])(v'irance , as described by Wkismann and others, may lead to the 

 production of a nuilc-egg, capable of developniont. 



2) From this it would seem to follow, that the four spermatozoa are 

 alike in all their fundamental characters (in their hereditary features), 

 and the same must bo true of the actual egg and its throe polar bodies. 

 That is to say, the four gametes, derived from any particular oocyte 

 or spermatocyte, must be identical. 



3) WoiiTEKKCK has already interpreted the synapsis as a suppressed 

 mitosis. He writes : "Gleichwohl scheint auch die Synapsis dos Cypris- 

 ovars mit einer Theilung in Verl)in(Uing zu stehen, welche jedoch nicht 

 mehr, wie dies Häckmu für Canthocamptus annimmt, zur Durchführung 

 kommt, sondern vielloii-ht eine unterdrückte mitotische Thei- 

 lung darstellt." (Zur Bildung und Entwicklung des Ostracodeneies, 

 in: Z. wiss. Zool., V. 04, p. t)!)!!— G28, 'J jilates, 1. c. p. (Uö.) 



