600 PROFESSOK MARCrS HAETOG. 



the progamic fissions are usually on the part of the female. 

 Moreoverj not to deprive the female of its essential character of 

 size the progamic fissions are usually of the unequal type we 

 have already noted in the Metazoan egg and in some Wracks 

 (as well as in many isogamous forms). 



In the Conferva (Edogonium the oosphere is differ- 

 entiated by transverse fissions producing a vertical row, of 

 which the upper cell is the oosphere, the rest sterile cells. 

 The same is the case with the Characese. Again, in the 

 Archegoniate Cryptogams the sperms have to be formed well 

 in advance to be ready for the conditions for their discharge and 

 travel to the archegone, or flask-shaped body in which lies the 

 central cell. This cell undergoes two divisions, both unequal. 

 The first division early forms a small cell, Avhich lies in the 

 neck (and may again divide), " neck-canal-cell," and a central 

 cell which fills the belly ; this last only undergoes its unequal 

 division vei'y late under those very conditions that determine 

 the travel of the sperms. The lower cell is here the oosphere, 

 and the upper is an abortive cell known as the belly-canal- 

 cell from its position at the apex of the belly of the flask. 



In Flowering Plants the males and females are really homo- 

 logous with the corresponding organs of the Cryptogams just 

 mentioned, though certain difficulties of interpretation still 

 exist. The pollen-grain and the embryo-sac are both formed 

 a good while in advance, as each has to be ready on its side 

 for the complicated process of pollination (including the 

 growth of the pollen-tube, and therefore the complex of cells 

 in the embryo-sac) all naked, and including the oosphere, 

 have arisen by early divisions. The pollen contains two 

 nuclei — a " vegetative " and a " generative " nucleus — during 

 the dowugrowth of the pollen-tube : the vegetative nucleus 

 is in advance, and is connected with the growth of the tube 

 and travel of the protoplasm ; the generative nucleus divides 

 in the tube itself into two, clearly homologous with the sperm- 

 nuclei of the Fern, and are carried down to the embryo-sac 

 without performing any organic function to disturb their con- 

 dition of youth before fusing with the oosphere. It was the 



