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SCIENCE 



[N. S. Vol. XXVI. No. 676 



bility which Morgan does not mention, viz., 

 that the visible nuclear phenomena, e. ff., size 

 and behavior of chromosomes, etc., axe results 

 or incidents of processes which are themselves 

 the real determinative factors. If we adopt 

 and consistently maintain a physiological as 

 opposed to a morphological point of view, we 

 are, it would seem, forced to this position. 



In conclusion, moi-phological and physiolog- 

 ical conceptions of sex are contrasted, the 

 author favoring the latter: 



The average equality of males and females in- 

 dicates, I think, that external conditions do not 

 regulate the result, but that some internal physi- 

 ological mechanism exists that determines the sex. 

 This physiological mechanism does not involve the 

 separation of male and female elements or units 

 in the egg and sperm, but only involves the pro- 

 duction of those conditions that determine whether 

 one or the other sex will develop. In some cases 

 the initiatory process may exist in the egg, in 

 others in the sperm, and in still others after the 

 union of egg and sperm (pp. 422, 423). 



The final section of the book, on secondary 

 sexual characters, comprises a brief account 

 of the data on the correlation between these 

 characters and the ovary and testis, and a 

 discussion of the theories of the origin of 

 secondary sexual characters. 



The book as a whole is largely, as any such 

 book must be, a compilation of facts. The 

 author deserves the commendation of all biol- 

 ogists for his attempt to bring together the 

 scattered data in so many different fields of 

 experimental zoology. But the concentration 

 of material within the limits of a single vol- 

 ume has necessarily resulted in a rather sum- 

 mary treatment of various subjects and entire 

 omission of others. Moreover, since the au- 

 thor has felt himself obliged to omit all con- 

 sideration of experimental embryology, form- 

 regulation and animal behavior, his consider- 

 ation of certain subjects is somewhat one- 

 sided. Many of the facts in all these fields 

 have a most important bearing on the prob- 

 ^ms of heredity and evolution and one which 

 still awaits consideration. 



The material which is presented is not al- 

 ways fully digested. Many of the chapters 

 read like a part of some " Jahre^bericht " and 



in many cases the reader is left to go over the 

 data of the experiment and work out the re- 

 sults for himself instead of finding them pre- 

 sented clearly and briefly. 



Bibliographies are appended to the various 

 chapters, but no direct references to these 

 bibliographies are made in the text. The dis- 

 advantages of this omission are obvious. In 

 many cases also the bibliographies are far 

 from being complete. 



As regards the numbering of the figures 

 confusion exists in several cases. Many of 

 the figures are groups of separate figures: the 

 groups are designated " Fig. 1," " Fig. 2," 

 etc., and the single figures are also numbered, 

 beginning with " 1 " in all cases except in 

 Figs. 3 and 5, where the numbers continue 

 from the preceding figures. In referring to 

 the figures no distinction is made in most 

 cases between the group and the single figure, 

 so that a reference to Fig. 4, for example, 

 may mean either the group Fig. 4 or the single 

 figure 4 in any of the groups. The explana- 

 tions of the figures make this confusion less 

 serious than it would be otherwise, but some 

 other system is certainly preferable. 



Style and method of presentation present 

 certain features which can be due only to 

 haste or lack of care. Repetition is not in- 

 frequent; for example, the two following sen- 

 tences appear within two pages of each other 

 and in reference to the same experiments of 

 Weismann : 



He believed that his observations and experi- 

 ments show that external factors do not determine 

 the appearance of the sexual generation (p. 337). 



Weismann carried out some experiments which 

 show, he thinks, that external conditions do not 

 regulate the alternation of generations ( p. 339 ) . 



And again in the account of the work of 

 Kellogg and Bell on sex determination in 

 silk-worms these two sentences are half a page 

 apart : 



The chief interest of their work is their exam- 

 ination of the possible effects of nourishment on 

 the second generation (p. 377). 



The possible influence of food in determining 

 the sex of the egg (or sperm) was also examined 

 (p. 378). 



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