596 PROFESSOIi MARCUS HAllTOO. 



and incomplete np till the first coil-division^ and, indeed, the 

 two constituent halves of the successive nuclei along the new 

 nuclear line may for a long series of divisions show their dis- 

 tinctness more or less defined. This delay is clearly a derived 

 and not a primitive phenomenon, and may be perhaps 

 explained by the acceleration or precocity of the germination 

 of the oosperm in Higher Animals and Plants, 



One at least of the two pairing-cells is often the product of 

 a cell-division or a series of one or more preceded by a series 

 of cell-divisions immediately preceding the fusion: these 

 are the "progamic fissions/' which we have now to consider. 

 When the syngamy is bisexual, either the male cells or the 

 female cells, or both, may be the produce of such progamic 

 divisions. The special type most familiar to zoologists as 

 universal in Metazoa (with the possible exception of the 

 Alcyonarians) is the so-called " maturation of the Qg^.^' The 

 large cell gorged with reserves, produced in the ovary, divides 

 into two, the one with the greater part of the cytoplasm and 

 retaining the " egg^' character, the other with a minute 

 cytoplast, though its nucleus is the counterpart of the other. 

 The former cell then undergoes a similar unequal fission, and 

 the larger cell is now the actual female pairing-cell, or 

 '^oosphere," often termed the "mature egg;'' and the two 

 small cells are called the "first" and "second polar bodies " 

 respectively (the first polar body may also divide into two). 

 This process may even be delayed until the entrance of the 

 sperm into the egg. At the very commencement of the 

 modern cytological study of fertilisation, in the late '70's, 

 Biitschli, Giard, and Mark independently interpreted these 

 divisions as the reversion to a protistic type of reproduction, 

 to form a brood of four reproductive cells, the one functional, 

 the other three abortive. This view sank into neglect before 

 suggestions made a little later by Balfour and by Minot, who 

 regarded the process as one of elimination into the small 

 cells of something interfering with reproduction by syngamy. 

 An adaptation of their views by Weismann led to the identifica- 

 tion with this of over half a score of non-homologous " reduction 



