io8 THE EVOLUTION OE SEX. 



between the modes of division of these homologues seems thereby even dis- 

 puted, much less shaken. The widely different conditions in which these two 

 processes occur, and their very different meaning to the organism, are of course 

 as obvious to us as to any; but here, as elsewhere, the moqmologist's com- 

 parisons are strictly independent of the approval of the physiologist. 



VI. Further Comparison of Ovum and Sperm. — It is often said that the 

 sperm is the male cell which corresponds to the ovum. This is only true in a 

 certain sense. In function the two elements are indeed, in a general way, of 

 equal rank, and are obviously complimentary. But even in this respect, the two 

 elements, which unite in equal proportions in the essential act of fertilization, are 

 not exactly sperm and ovum, but [a) the head or nucleus of the sperm and (b) 

 the female nucleus doubly reduced by the extrusion of two polar globules. The 

 accurate structural resemblance or homology is not between ovum and sperm, 

 but between ovum and mother-sperm -cell.* This fact, pointed out by Reichert 

 in 1847, corroborated by Von la Valette St. George, Nussbaum, and others, is 

 fundamental to a clear comparison of the history of ovum and sperm, and is pos- 

 tulated as an accepted fact in the rationale of spermatogenesis suggested in this 

 chapter. It is possible to follow out the homology into even further detail ; 

 thus the antithesis seen in polor-globule formation may be fairly collated with 

 similar separations occurring in spermatogenesis. 



Van Beneden and Julin, in their researches in 

 oogenesis and spermatogenesis in Ascaris, have 

 noted the morphological correspondence of the 

 polar globules, as we may call them, of both 

 ovum and sperm. Again we have a recent micro- 

 chemical demonstration of the similar staining Fig. 31.— Diagrammatic comparison- 

 reactions Of polar globules in Ova, and the COtTe- *■ female <M and male ,*1 cell formed 

 ,. r ,, n . from the division of a single cell in 



sponding remnant of the parent cell in sperma- the development of the hermaphro . 



genesis. In the differentiation of the reproduc- dite reproductive organs of the worm 



tive cells in plants, both higher and lower, simi- Sagitta ; II. ovum <w and polar 



lar extrusions are to be observed. Of this ° y a '„ ... ' f J / np 



sperm-cell o>> and the spermatozoon 



Strasburger has given numerous illustrations, a z. 

 crowned by his own demonstration that the 



nucleus of the pollen grain, in its germination upon the stigma, separates into a 

 vegetative, relatively unimportant, and a generative or essential nucleus. Even 

 in Protozoa Blochman and others have found analogues. A process so general 

 is capable of a unified explanation, more specific than that of simply referring 

 the matter to the mysterious necessities of cellular physiology. Just as in the 

 development of the "worm" Sagitta a single cell divides into two, which 

 become the starting-points of male and female organs respectively, so the cell 

 divisions above alluded to express antitheses between more katabolic and more 

 anabolic protoplasmic constituents. 



VII. Chemistry of the Sperm. — Comparatively little has been done in 

 regard to the chemistrv of the male elements in different animals. The most 



* Since the above was written, Platner has in a remarkable manner demon- 

 strated the unity between the division of the ovum in extruding polar globules 

 and the division of the spermatocytes. In both cases occurs the unique phe- 

 nomenon of a second nuclear division following on the heels of the first without 

 the intervention of the usual resting phase. 



