SOME PROBLEMS OF REPRODUCTION. 597 



processes," and a succession of theories, of which it may 

 suflBce to say now that they have had their day. One ground 

 for these theories is the fact that in Metazoa, where progamic 

 divisions were first studied, they are marked by their coinci- 

 dence with the heterotype mode of nuclear division, and 

 eventuate in the reduction of the number of chromosomes in 

 the pairing-cells to half of that obtaining in the tissue-cells 

 (to be doubled anew by the fusion of two cells to form the 

 oosperm and the new being). When, however, it was seen 

 that reducing visions occur to produce the tetraspores of 

 the Archegoniate Cryptogams (as also of the Sphacelariese), 

 which do not pair, but germinate into distinct plants, from 

 the tissues of which the pairing-cells are only produced after 

 long tissue-generations, it became obvious that " progamic 

 fissions " and " reducing divisions " are phenomena distinct, 

 though sometimes coincident, and that a separate explanation 

 was needed for the former. 



Oscar Hertwig, in 1890, showed that in Ascaris the 

 "maturation divisions" of the egg are absolutely homologous 

 with those that form a brood of four equal sperms in the 

 male. In a paper completed a year later I showed by com- 

 parison with numerous data that the view of the three oldest 

 observers was alone tenable. In 1895 Oltmanns described a 

 process in the Wracks (Fucacoce) comparable with the forma- 

 tion of the polar bodies, but of crystalline transparency when 

 the different species were collated. 



The oogonial cell always divides into a brood of eight; in 

 some species these are all equal and functional oospheres; 

 in others four (4) are functional and four (4) abortive ; 

 in others two (2) are functional and six (6) abortive ; in 

 others, again, only one (1) is functional and the other seven 

 (7) are abortive. If additional proof were wanted it was 

 furnished recently by Francotte, who found that certain 

 marine Planarians have exceptionally large " polar bodies," 

 which may be fertilised by sperms like the " matured egg " 

 itself. Thus the morphology of the progamic divisions of 

 the egg of Metazoa is established; and generally such divi- 



