THE ORGANIC CELL 
45 
resulting larvse were of a form midway between that of the 
parents, showing certain characteristics of each. This hybrid 
formed a new type which was constant, and was never known 
to simulate either Echinus or Sphcerechinus to such a degree 
as to be mistaken for them. 
Four important factors are thus established : — 
1. The constancy of Echinus larval type. 
2. The constancy of S'phcerechinus larval type. 
8. The constancy of the hybrid between Echinus and 
Sphcerechinus ? . 
4. The ability to secure non-nucleated Sphcerechinus 
fragments which were capable of fertilisation. 
The final test would be to cross-fertilise non-nucleated 
portions of Sphcerechinus with Echinus sperm. The kind of 
larvae resulting from this cross would decide the question. 
If the resulting larvae are of a hybrid type, then both nucleus 
and cytoplasm determine the hereditary characters. If pure 
Sphcerechinus results, then the cytoplasm is the bearer of the 
hereditary qualities. Should, however, the result be of the 
pure Echinus type, then to the nucleus of the spermatozoon 
alone can be credited the power of determining the quality 
of the offspring. The larvae obtained by Boveri were of pure 
paternal or Echinus type, there being no taint whatever 
of the maternal element. The development of these larvae has 
been brought about solely by the nucleus of the spermatozoon. 
Thus by pure experimental evidence the chromatin material 
has been shown to be the physical basis of heredity, the cyto- 
plasm which is represented by Sphcerechinus having had no 
influence in determining the type of larva which results. 
The Nucleus during the Process of Maturation. 
The phenomena occurring during maturation bring out 
in quite as convincing a manner the great difference between 
cytoplasm and nucleus. The germ-nuclei undergo the ex- 
ceedingly complicated series of changes associated with chro- 
matin reduction, thus rendering them absolutely equivalent 
at the time of their union. When this fact is taken in con- 
junction with the result of the union of the germ-cells, which 
