FOUNDATION OF A THEORY OF HEREDITY. 223 



separates from the female germ-cell, reminds us, in every way, of 

 the polar bodies of animal eggs. Furthermore, the spermatozoids 

 in the mosses and vascular cryptogams throw off a small vesicle 

 before performing their functions 1 . On the other hand the equiva- 

 lents of ' polar bodies ' (the ' ventral canal-cells ') are said to be ab- 

 sent in the Cycads, although these are so nearly allied to Conifers. 

 Furthermore, 'no phenomenon occurs in the oospheres (ova) of An- 

 giosperms which can be compared to the formation of polar bodies.' 

 Strasburger therefore concludes that the separation of certain parts 

 from the germ-cells is not in all cases necessary for maturation, 

 and that such phenomena are not fundamental, like those of 

 fertilization, which must always take place along the same morpho- 

 logical lines. He further concludes that the former phenomena are 

 only necessary in the case of the germ-cells of certain organisms, 

 in order to bring the nuclei destined for the sexual act into the 

 physiological condition necessary for its due performance. 



I am unwilling to abandon the idea that the expulsion of the 

 histogenetic parts of the nuclear substance, during the maturation 

 of germ-cells, is also a general phenomenon in plants ; for the 

 process appears to be fundamental, while the argument that it 

 has not been proved to occur universally is only of doubtful value. 

 The embryo-sac of Angiosperms is such a complex structure that 

 it seems to me to be possible (as it does to Strasburger) that ' pro- 

 cesses which precede the formation of the egg-cell have borne 

 relation to the sexual differentiation of the nucleus of the egg.' 

 Besides, it is possible that the vegetable egg-cell may, in certain 

 cases, possess so simple a structure and so small a degree of histo- 

 logical specialization, that it would not be necessary for it to 

 contain any specific histogenetic nucleoplasm : thus it would con- 

 sist entirely of germ-plasm from the first. In such cases, of course, 

 its maturation would not be accompanied by the expulsion of 

 somatic nucleoplasm. 



I have hitherto abstained from discussing the question as to 

 whether the process of the formation of polar bodies may require 

 an interpretation which is entirely different from that which I 

 have given it, whether it may receive a purely morphological inter- 



[ x It is almost certain that this vesicle is not derived from the nucleus, but from 

 the cytoplasm of the sperm-mother-cell. See Douglas H. Campbell, 'Zur Ent- 

 wicklungsgeschichte der Spermatozoiden ' in Berichte der deutschen botanischen 

 Gesellschaft, vol. v, 1887, p. 122. S. S.] 



