SOME PROBLEMS OF REPRODUCTION. 589 



for mucli brilliant theorising, whicli of course fails now that 

 we see the double sense of the word. 



Before closing I would add a classification of the different 

 modes of brood-division. The first and simplest mode is the 

 ''direct" (''euthyschist") : in this case, as seen in the seg- 

 mentation of the frog's ogg, eacli division of the nucleus is 

 followed by that of the cytoplasm, so that at every stage the 

 brood consists of individual cells. The second is the 

 "delayed" (" bradyschist") type: liere the nuclear 

 divisions go on successively without any division of the cyto- 

 plasm till the nuclear divisions are completed. Thus the 

 brood-mother-cell passes for a time into the condition of an 

 apocyte, and is finally resolved into single cells by more or 

 less simultaneous segmentation of the cytoplasm. A modifi- 

 cation of this process is that of schizogony, which usually 

 occurs when the brood-cells have a particular configuration, 

 like sperms generally and the zoospores of the Ooccidians ; 

 the cytoplasm around each nucleus grows out almost into 

 the perfect form of the brood-cell to be freed while still 

 continuous with a mass of common cytoplasm, the " cyto- 

 pliore/' which may be central, as is most frequent, or ex- 

 centric, as in the case of the zoospores of Noctiluca, where 

 the cytophore is enormous, and the sperms of many Metazoa. 

 " False brood -for mat ion," takes place Avhere the ante- 

 cedent is not a single cell, but an apocyte which has discharged 

 living functions, as in the case of the zoosporange oP Sapro- 

 legniese or the sporange of Mucor: this becomes resolved 

 into single cells by the cleavage (whether simultaneous or con- 

 secutive) of the cytoplasm between the single nuclei. These 

 modes, I think, comprise most of the processes by which single 

 reproductive cells (spores, gametes, etc.) are foi-med, or 

 colonial aggregations of cells, as in the segmenting oosperm, 

 or the VolvocineiB. In eggs provided with abundance of food- 

 yolk, as the hen's egg, there may be a combination of the direct 

 type, giving single cells, and the delayed type, producing the 

 apocytial condition of the yolk below the young blastoderm. 



