228 CONTINUITY OF THE GERM-PLASM AS THE [IV. 



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 matura- 

 tion 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 'processes which precede the formation 

 of the egg-cell have borne relation to the sexual differentiation 

 of the nucleus of the ^gg! Besides, it is possible that the 

 vegetable egg-cell may, in certain cases, possess so simple a 

 structure and so small a degree of histological specialization, 

 that it would not be necessary for it to contain any specific 

 histogenetic nucleoplasm : thus it would consist 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 mor- 

 phological interpretation. In former times it could only be 

 regarded as of purely phyletic significance : it could only be 

 looked upon as the last remnant of a process which formerly 

 possessed some meaning, but which is now devoid of any 

 physiological importance. We are indeed compelled to admit 

 that a process does occur in connexion with the true polar 

 bodies of animal eggs, which we cannot explain on physio- 

 logical grounds ; I mean the division of the polar bodies after 

 they have been expelled from the ^gg. In many animals the 

 two polar bodies divide again after their expulsion, so as to 

 form four bodies, which distinctly possess the structure of cells, 

 as Trinchese observed in the case of gastropods. But, in the 

 first place, this second division does not always take place, and, 

 secondly, it is very improbable that a process which occurs 

 during the first stage of ontogeny, or more properly speaking, 

 before the commencement of ontogeny, and which is, therefore, 

 a remnant of some excessively ancient phyletic stage, would 



