114 THE EVOLUTION OF SEX. 



Difficulties become thick, however, when we inquire into the division 

 of the niother-sperm-cell or spermatogonium, and it is here that the observa- 

 tions of recognised authorities so much disagree. Accepting the results of 

 competent observers, we have elsewhere endeavoured to rationalise and 

 unify the conflicting observations, by comparing the different modes of 

 spermatogenesis with the different forms of ovum-segmentation. It has 

 been already incidentally noticed, that the egg-cell may divide wholly and 

 equally, or unecjually, or only very partially, or round a central core. 

 Just in the same way the mother-sperm-cells may divide into a uniform 

 ball of cells, or only at one pole, or only at the periphery round a central 

 residue. Balfour and others had hinted at this comparison in the use of 

 terms like sperm-morula; and Herrmann had also concluded, " that the 

 division of the male ovule into a series of generations of daughter-cells, is 

 a phenomenon comparable to that exhibited by the ovum in the formation 

 of the blastoderm. ... It seems then more important to determine 

 exactly the mechanism of division, than to give a particular name to each 

 stage of segmentation." 



Although this interpretation of spermatogenesis by collating it with 

 ovum-segmentation appears to Minot "a fanciful comparison," in favour of 

 which he is "unable to recognise any evidence," neither the initial 

 homology between the mother-sperm-cell and ovum with which we start, 

 nor the striking parallelism between the modes of division of these 

 homologues seem thereby even disputed, 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 morphologist's comparisons are strictly inde- 

 pendent of the approval of the physiologist. 



§ 6. Further CoiJipa7-ison of Ovum 



and Sperm.— \i 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 ele- 



j[ jij; ments are indeed, in a general way, of 



Diagrammatic comparison— I. female ^1 equal rank, and are obviously comple- 



and male a} cell formed from the mentary. But even in this respect, the 



division of a single cell in the de- two elements, which unite in equal pro- 



velopment of the hermaphrodite re- .• • ^r, .• i . r r ••!• 



productive organs of the worm po/^ions m the essential act of feriihs- 

 Sagitta; II. ovum b'^ and polar ation, are not exactly sperm and ovum, 

 body a'-\ III. stump of moth er- but {«) the head or nucleus of the sperm 

 sperm-cell^ and the spermatozoon a3. ^^^id (/;) the female nucleus doubly re- 

 duced by the extrusion of two polar globules. The accurate structural resem- 

 blance or homology is not between ovum and sperm, but between ovum and 

 mother-sperm-cell.* This fact, pointed out by Reichert in 1847, corrobor- 

 ated by Von la Valette St George, Nussbaum, and others, is fundamental to a 

 clear comparison of the history of ovum and sperm, and is postulated as an 

 accepted fact in the rationale of spermatogenesis suggested in this chapter. 



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

 demonstrated the unity between the division of the ovum in extruding 

 polar globules and the division of the spermatocytes. In both cases 

 occurs the unique phenomenon of a second nuclear division following on 

 the heels of the first without the intervention of the usual resting phase. 



