2 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



The eggs of a small number of species can develop " spon- 

 taneously/' but in the majority of animals no development is 

 possible until a male sex cell, the spermatozoon, enters the egg. 



2. The spermatozoon is a living motile organism, resembling 

 a certain class of protozoa, the flagellates. All the mystery 

 which surrounds the term "life" formerly surrounded also the 

 action of the spermatozoon upon the egg. The interest of the 

 experiments reported in this book lies in the fact that they 

 substitute the action of well-known chemical and physical 

 agencies for that of the mysterious complex called " living 

 spermatozoon." 



The spermatozoon has two kinds of effects upon the egg: 

 in the first place, it causes its development, and secondly it 

 transmits the paternal characters to the developing embryo. 

 Now it is probable that the developmental and hereditary 

 effects of the spermatozoon are connected with different 

 materials contained therein. For it is possible to fertilize the 

 eggs of the sea-urchin with the spermatozoa of quite different 

 species or genera, e.g., starfish, brittlestars, holothurians/ 1 

 crinoids, 2 and even of mollusca (Mytilus* and Chlorostoma*) . 

 Strangely enough, however, all these cases of heterogeneous 

 fertilization give rise to the development of a typical sea- 

 urchin larva, viz., a pluteus; hence the spermatozoon exerts 

 here only a developmental, but no hereditary, effect. These 

 experiments show that we must distinguish between the develop- 

 mental and the hereditary effect of the spermatozoon, and 

 that each of these effects depends probably upon different 

 materials in the spermatozoon. 



In this treatise we shall consider only the developmental 

 effect of the spermatozoon; or rather, we will describe 



1 Loeb, Untersuchungen zur kiinstlichen Parthenogenese, Leipzig, 1906, pp. 382- 

 483; Pfliiger's Archiv, XCIX, 323, 1903; CIV, 325, 1904. 



2 Godlewski, Archiv f. Entwicklungsmechanik, XX, 579, 1906. 

 s Kupelwieser, Biolog. Centralbl, XXVI, 744, 1906. 



4 Loeb, Archiv f. Entwicklungsmechanik, XXVI, 476, 1908. 



