52 WYMAX REED GREEN". 



tinu- thr recorded opinions range all the way from unconditional 

 j nance of his extreme view to a complete lack of faith in it. 

 r convenience of discussion these various views may, in 

 general, be grouped under two chief heads: 



i. That external factors are of little or of no importance in 

 relation to the succession of periods of parthenogenetic and 

 sexual reproduction. This was the conviction of Weismann, 

 based upon his researches extending over a long period of years. 

 This theory was broad enough to cover all forms of life in which 

 there is a succession of parthenogenetic and sexual reproduction. 

 Accordingly the evidence for the theory extends over a wide 

 field, and it has numerous supporters, having been for a long 

 time the orthodox view. 



This general view is supported by Keilhack (1906) and Ekman 

 (1905) working on Polyphemus, by Popoff (1907) working on 

 various protozoa and metazoa, and by Punnett (1906) and 

 Whitney (1907) working on Ilydatina, and by others. The 

 last two authors concluded tha-t the age of the strains is a weighty 

 factor in causing the appearance of the sexual forms. The con- 

 clusions of Strohl (1908) constitute a clean cut statement of the 

 views up to that time. Working with Polyphemus, he concluded 

 that there was no reason for abandoning the well grounded 

 views of Weismann. Kuttner (1909) working on Simocephahis 

 vettilus and other Daphnians adopted Weismann's extreme view. 

 McClendon (1910) considers that "The life cycle of a Daphnid is, 

 therefore an heredity tendency, but can be influenced by nutrition 

 and probably by temperature and the accumulations of ex- 

 cretions," and he adds "Nutrition is the most important factor." 



The extended experiments of Woltereck (1909-1 1) on Cladocera 

 led 'him to admit automaticity as one of the factors in determining 

 the course of their life cycle. Assuming that Woltereck's cul- 

 tural conditions (1911, fig. 4, p. 152) were kept the same in all 

 four cultures for the full four years, one would be forced to the 

 conclusion that there are periods when environmental lactors 

 are of no influence, and possibly other periods when they are, 

 since the four cultures responded not only differently in different 

 years, but different cultures responded differently in the same 

 rs; in other words, the conclusion would seem to follow that 



