NEW TYPES OF CHROMOSOME DISTRIBUTION. l6l 



determination of universal application, the parthenogenetic forms 

 have been more or less of a stumbling block. The above results 

 are in perfect harmony with the hypothesis of sex-production 

 advocated by McClung, Stevens and Wilson. 



Morgan also gives some further observations, indicative as to 

 the manner in which males and sexual females are produced from 

 parthenogenetic eggs. " I find that the somatic cells of the males 

 of the species referred to above contain only five chromosomes. 

 These five give in the spermatogenesis the reduced number three 

 by two uniting with each other and the third having no partner. 

 I find that the somatic cells of the female contain six chromo- 

 somes. It follows that at some time in the life cycle of the 

 parthenogenetic eggs, one chromosome disappears in those eggs 

 that become males, while the full number is retained in the female. 

 It seems plausible that this change takes place in the formation 

 of the single polar body given off by the parthenogenetic egg. 



; The results seem to show that while the sex of the stem 

 mother is connected with the presence of ' female-producing ' 

 spermatozoa, the production of males and of sexual females is 

 dependent on a process that takes place in the egg analogous to 

 the same process that takes place in the spermatogenesis of other 

 kinds of insects. Hence it follows that the egg as well as the 

 sperm has the power of determining sex by regulating the number 

 of its chromosomes." 



Von Baehr's recent results ('08) and also those of Stevens 

 ('09) on the aphids confirm those of Morgan on the phylloxerans. 



In a preliminary note ('08) Baltzer gives some results on 

 echinoderm eggs, where he finds in the early cleavage stages of 

 fertilized eggs of Echinus microtuberculatus and Strong\locen- 

 trotus lividiis, an unpaired element which comes from the egg 

 nucleus. Further, this unpaired element is present in only a 

 part of the eggs. He suggests the possibility that this may be 

 a chromosome which has to do with sex determination. If this 

 element should prove to be a chromosome and in one half of the 

 eggs, it would be the reverse of the condition found in the insects, 

 for there the unpaired chromosome has arisen in the male. 

 However, two such diverse phenomena are not impossible in 

 different groups of animals, as we have no reason to suppose that 



