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. Al! 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,! 
erinoids,? 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. 
3 Kupelwieser, Biolog. Centralbl., XXVI, 744, 1906. 
4 Loeb, Archiv f. Entwicklungsmechanik, X XVI, 476, 1908. 
