399 



long period in which they do not divide, is a matter of relatively little 

 importance. Great fluctuations are found and many of the totals can 

 not be construed as powers of 2. Even allowing for degeneration of 

 sex-cells and possible errors in counting, one is utterly unable to class 

 the major part of these totals, as approximating 256, 512, 1024, or 

 2048, the greater part of them falling well between those figures. 



Driesch, '98 and '05, Bovert, '03, and Peter, '06, have all shown 

 that there is a great degree of variation in the number of primary 

 mesenchyme cells in various echinoderms studied by them. Peter, '06, 

 shows that the number of these cells in Echinus microtuberculatus 

 may vary all the way from 40 to 86. He supports the theory of 

 pure maternal characters by a series of counts, in which the eggs 

 taken from a given female, develope into larvae whose average number 

 of primary mesenchyme cells is characteristic of the maternal parent. 

 These observations clearly tend to support certain conclusions which 

 we have drawn from the data given above, namely, that there is a 

 wide range of variation in the number of sex-cells found in any given 

 embryo during the stages studied, and that there is a more restricted 

 range of variation in embryos of the same parentage, than in those 

 of dissimilar parentage. 



Bibliography. 



Beard, J., '02, The Numerical Law of the Germ-cells. Anat. Anz., 

 Bd. 21, 1902. 



— , '02, The Germ-cells of Pristiurus. Ibid. 



— , '04, The Germ-cells. Journal of Anatomy and Physiology, Vol. 38, 

 1904. 



BovERi, T. H., '03, Ueber den Einfluß der Samenzelle auf die Larven- 

 charaktere der Echiniden. Arch. f. Entwickelungsmechanik, Bd. 16, 

 1903. 



Driesch, H,, '97, Von der Beendigung morphogener Elementarprozesse. 

 Arch. f. Entwickelungsmechanik, Bd. 6, 1897. 



— , '98, Ueber rein mütterliche Charaktere an Bastardlarven von Echi- 

 niden. Ibid., Bd. 7, 1898. 



— , '05, Ueber das Mesenchym von unharmonisch zusammengesetzten 

 Keimen der Echiniden. Ibid., Bd. 19, 1905. 



Eigenmann, C. H., '96, Sex-differentiation in the Viviparous Teleost 

 Cymatogaster. Arch. f. Entwickelungsmechanik, Bd. 4, 1896. 



Peter, Karl, '06, Ein Beitrag zur Vererbungslehre. Ueber rein mütter- 

 liche Eigenschaften an Larven von Echinus. Deutsch, med. Wochen- 

 schrift, 1906, No. 31. 



