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abortive germinal vesicles in Claclocera as contribnting to the 

 deutoplasm ; but wc think a Avide distinction ought to be 

 drawn between such deutoplasm and that which is jjouved 

 round the cell-egg from a distinct gland. From the above 

 remarks, it appears there is much the same obscurity in 

 plants as in animals with regard to the relation of the germinal 

 vesicle to fertilisation, i. e., whether the egg has a nucleus 

 before fertilisation which persists and divides into the nuclei 

 of the embryonal-cells — in all cases alike — and if so, how the 

 apparent absence of such a nucleus at the moment of fertili- 

 sation in particular classes is to be explained. One thing- 

 may well be remembered in this matter : we have no right 

 to lay any great stress on the mere formal structure of a cell, 

 and the nucleus must be regarded as important only so far as 

 we see it in direct connection with important phenomena. 

 Morphologically it is but the central slightly differentiated 

 part of a lump of viscid matter. Now Ave have in the non- 

 nucleated red blood-corpuscles of mammalia and the nucleated 

 red corpuscles of all other vertebrata a remarkable instance of 

 the Avay in which structural units, undoubtedly of the same 

 origin and signification in the tAvo cases, may put on different 

 appearances, and it seems to be just j^ossible that Avith as 

 little significance as the absence or the differentiation of a 

 ' nucleus ' is brought about in these two cases, may the 

 absence or presence of a nucleus in the cell-egg at the 

 moment of fertilisation be produced. This is one Avay of 

 looking at the matter, but another is suggested to us by 

 Dr. Van Beneden's exi^osition of the fusion of the deuto- 

 plasm Avith the original protoplasm of the cell-egg, Avhich 

 seems to be Avorth consideration. In the same Avay as the 

 protoplasm of the cell-egg is found in some cases to be 

 thoroughly fused Avith the deutoplasm, and in other cases 

 distinct, may not the nucleus of the same ovum become at a 

 certain epoch of its groAvth, under certain chemical and 

 physical conditions, diffused or mixed up Avith the surround- 

 ing matter temjjorarily, again, contracting, segregating and 

 assuming its nuclear form after a time, that is, after the first 

 contraction of the yelk-cleavage has shoAvn itself. Haeckcl, 

 in a recent very interesting ' Essay on the Plastid and Cell 

 Theories,' suggests that Ave may see in the disappearance of 

 the germinal vesicle of the cell-egg, a return to that elemen- 

 tary ancestral form Avhich must be admitted as preceding the 

 cell, namely, the cytod, the structureless mass of j^rotoplasm 

 Avith membranous pellicle or Avithout, Avliich he has shoAvn to 

 be the character of several Avell marked forms, his Monera. 

 The other and more intelligible form of velk- cleavage, in Avhich 



