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POPULAR SCIENCE MONTHLY 



may be traced to antecedent conditions 

 that preexist in the germ-cells before 

 their union. In most of the species 

 the spermatozoa are predetermined as 

 male-producing and female-producing 

 forms, equal in number, that differ 

 visibly in the constitution of the nuclei. 

 The differences between the two classes 

 do not appear in the mature sperm- 

 atozoa but are plainly apparent in the 

 process of their formation. In some 

 cases the female-producing spermatozoa 

 contain one more chromosome than the 

 male-producing ones, in others both 

 classes have the same number of chro- 

 mosomes but one of them is much 

 smaller in the male-producing class. 

 These initial differences in the sperm- 

 atozoa lead to corresponding differences 

 in the nuclei of the two sexes, the cells 

 of females either containing one more 

 chromosome than those of males or 

 showing a greater quantity of chromatin 

 in the greater size of one of the chro- 

 mosomes. The sex of the individual 

 may, therefore, be recognized in these 

 cases by simple inspection of the divi- 

 ding cells. 



Although these visible differences are 

 of wide occurrence in these insects 

 they are not always present, for in one 

 of the genera male-producing and fe- 

 male-producing spermatozoa can not be 

 distinguished by the eye and the nuclei 

 of the two sexes have the same appear- 

 ance. This case is, however, connected 

 by almost insensible gradations with 

 those in which the differences are 

 plainly apparent, and it is hardly pos- 

 sible to doubt that sex-production con- 

 forms to the same type throughout the 

 series. It is, therefore, not improbable 

 that two classes of spermatozoa, pre- 

 determined as male-producing and fe- 

 male-producing forms, may exist in ani- 

 mals generally, even though they are 

 not, as a rule, visibly distinguishable. 



It is not yet known whether this also 

 applies to the eggs before fertilization. 

 In these insects there is no visible indi- 

 cation of such a predetermination, but 

 several eases are known in which the 

 eggs are of two sizes before fertiliza- 



tion, the larger ones producing females 

 and the smaller ones males. It is, 

 therefore, possible that in animals gen- 

 erally, both eggs and spermatozoa may 

 be predetermined as male-producing 

 and female-producing before their 

 union. In any case these observations 

 bring a strong support to the view, 

 which has rapidly gained ground in 

 recent years, that sex is predetermined 

 at least as early as the fertilized egg, 

 though they do not exclude the pos- 

 sibility that in some cases sex may be 

 affected by conditions acting upon the 

 embryo subsequent to fertilization. It 

 does not yet clearly appear how these 

 new results can be applied to ah ex- 

 planation of sex-production in partheno- 

 genesis, in hermaphrodites and in such 

 cases as that of the bee where all the 

 fertilized eggs are of the same sex. 

 A new basis has, however, been gained 

 for the investigation of these questions, 

 and also for an interpretation of sex- 

 production in accordance with the 

 Mendelian principles of heredity, the 

 probability of which has been urged by 

 Castle, Bateson and other writers. 



TWO GERMAN DIRECTORIES 

 There appeared in November the 

 fifteenth annual edition of 'Minerva' 

 and a little earlier a German ' Wer 

 Ist's.' The former of these works 

 is well known to scholars throughout 

 the world. It is an invaluable address 

 book containing the names and chairs 

 of the professors in the universities 

 and other institutions of higher educa- 

 tion of all countries, the officers of 

 libraries, museums, academies, etc., and 

 much information in regard to the or- 

 ganization of these institutions. The 

 editing is a model of careful exactness; 

 it requires some search to find a mis- 

 spelled name among the 40,000 in the 

 book. The work is brought out with 

 unusual promptness. It appeared 

 early in November and contains changes 

 up to October. Each year a portrait 

 of an eminent scholar is given as a 

 frontispiece. This year Dr. Sophus 

 Muller, director of the National Mu- 



