THE DETERMINATION OF SEX lOI 



of Baltzer, the sex of Echini is determined not by the spermato- 

 zoa but by the egg. According to him, the Echini have two 

 kinds of eggs which differ in their chromosome relations. 



The investigation of the determination of sex must be 

 pursued much further. It is above all important to ascertain 

 whether the conditions which have been discovered in insects 

 recur in all animals and plants. We ask at the same time, 

 what are the relations in hermaphrodites? We cannot at 

 present even guess the answer to this question. 



It must also be distinctly emphasized that the causal 

 relations are not clear. We have learned through the 

 memoirs which have been cited that the nuclei of a female in 

 a considerable number of animal species contain more chroma- 

 tine than the nuclei of a male. We are unable, however, to 

 bring this peculiarity into causal relation with the difference 

 of sex. It is quite possible that the excess of chroma tine is 

 only the expression of more essential peculiarities, although 

 the greater probability remains that the accessory chromo- 

 some is the material cause and basis of sex. 



Mortiz Nussbaum considered the two sexual elements as 

 homologous. He wrote in 1880: "Es treten somit bei der 

 Befruchtung nicht zwei heterogene Elemente zusammen, die 

 einander erganzen und .... es treffen sich vielmehr 

 zwei homologe Zellen, von denen die eine zum Zweck der 

 Konjugation sich in eine beweglichere Form umgegossen hat." 

 The homology of the mature ovum with a spermatozoon has 

 been generally accepted. The new investigations make this 

 doubtful. 



We know at present four different species or types of cells. 

 Two types are diploid, that is to say, they have the full num- 

 ber of chromosomes; and two types are haploid, that is to 

 say, they possess the reduced number of chromosomes. 



