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THE AMERICAN NATURALIST 



[Vol. XLV 



another in oogenesis is unknown. Boveri makes several sugges- 

 tions without adopting any of them as (1) position of the cells in 

 the egg-tube, (2) seasonal conditions (sperm-production occurs 

 first, egg-production later), (3) unequal plasmatic cell-divisions 

 in the young worm, differentiating sperm-producing from egg- 

 producing tissue. 



As regards hermaphroditic animals in general, Boveri main- 

 tains that these, when they have the secondary characters of one 

 sex only have that of the female rather than of the male, citing 

 as examples gastropods and eirripeds. Females may retain the 

 capacity to develop sperm, hut males do not retain the capacity 

 to develop eggs. For the male state is due to retrogressive varia- 

 tion, loss of cell-constituents, as for example of an x-chromosome. 

 Now in the female this loss may occur in certain reproductive 

 cells only, which then become reproductive cells of the male, i. e., 

 spermatozoa. But in the male individual, since all its cells are 

 in the reduced state, reproductive bodies characteristic of the 

 female (eggs) can not be produced. Nevertheless the male, 

 though unable to form eggs ( which we may assume can come 

 only from a 2x cell) is able to form female-producing gametes, 

 those with the full half number of chromosomes. 



In its bearing on general theories of sex-determination 

 Boveri 's paper is important. It provides a way of reconciling 

 the opposed views that sex-determination is independent of 

 environmental influences and that it is dependent upon them. 

 Both views are correct in part. 



Sex is apparently in all cases controlled by cell structure, a 

 clear index of which is afforded by the number of the chromo- 

 somes found in the nucleus. The more complete, or fully duplex, 

 state is in all cases characteristic of the female : a more reduced 

 state, either partially duplex or simplex, is characteristic of the 

 male. But external conditions may influence the cell-constitu- 

 tion, and so indirectly determine sex. This is known to be the 

 case in parthenogenesis and according to Boveri 's observation in 

 this paper it may be true in hermaphroditism also. Thus in 

 rotifiers and daphnids abundant nutrition causes the unfertilized 

 egg to develop without undergoing reduction, i. e., in the fully 



tion is complete and it has passed into the simplex condition, and 

 a male results. The protoplasmic differences in the two cases 

 are not confined to differences in chromosome number, the cell 



duplex (2N) 

 causes the unf 



d 



