INCOMPLETE HETEROGAMY. 131 



reproductive process is of the greatest interest as throwing light 

 upon the way in which the phenomena of alternation of generations 

 and heterogamy may have arisen in that it appears in a certain degree 

 as the precursor of the alternating sequence of two or more genera- 

 tions of individuals. The so-called alternation of generations in the 

 stone-corals (Blastotrochus), which in early life reproduce themselves 

 by budding, without thereby losing the power of acquiring sexual 

 organs at a later period of life, forms an example of this method of 

 reproduction. 



In this category of incomplete heterogamy should be placed the 

 reproductive processes of the Phyllopoda and Rotifera, in which the 

 female produces summer eggs capable of parthenogenetic develop- 

 ment, and later winter eggs requiring fertilization (Daphnidce). 



[In the above account the term alternation of generations, or 

 metagenesis is applied to those cases in which sexual and asexual 

 generations alternate ; while heterogamy is applied to those cases 

 in which two sexual generations or a sexual and parthenogenetic 

 generation alternate.] 



CHAPTER IV. 



HISTORICAL REVIEW.* 



THE origin of Zoology extends far back into antiquity. Aristotle 

 (4th century B.C.), who scientifically and in a philosophic spirit 

 worked up the experiences of his predecessors with his own extended 

 observations, must be looked upon as the founder of this science. 

 The most important of his zoological workst treat of the " Repro- 

 duction of Animals," of the " Parts of Animals," and of the " History 

 of Animals." The last and most important work is, unfortunately, 

 only incompletely preserved. 



We must not expect to find in Aristotle a descriptive zoologist, 

 nor in his works a system of animals followed out into the smallest 



* Victor Cams, " Geschichte der Zoologie." Munchen, 1872. 



f Compare Jiirgen Bona Meyer's " Aristoteles' Thierkunde " (Berlin, 1855). 

 Frantzius, " Aristoteles' Theile der Thiere " (Leipzig. 1853). Aubert und 

 Wimmer, " Aristoteles' Fiinf Biicher von der Zeugung und Entwicklung der 

 Thiere, iibersetzt und erlautert" (Leipzig. I860). Aubert und Wimmer, 

 " Aristoteles' Thierkunde." Band I. und II. (Leipsij, 1868). 



