IOO THE EVOLUTION OF SEX. 



process, as interpreted by him, seemed to mark out the extrusion as something 

 unique. The latest results of Boveri, Zacharias, and others, however, confirm 

 the older view, that the process is essentially one of normal cell-division. 



But while this structural fact may be regarded as certain, there is no 

 unanimity as to what the process means. The chief opinions on this subject, 

 only a mere outline of which can be given, are three, not including a number of 

 suggestions according to which the extrusion of the globules is a kind ot 

 "excretion" of the ovum, or a "rejuvenescence" of the nucleus. 



(a) According to some, the egg-cell is in a sense hermaphrodite, and the 

 polar-globule formation is an extrusion of the male element. Balfour expressed 

 his view in somewhat teleological language: "I would suggest that in the 

 formation of the polar cells, part of the constituents of the germinal vesicle, 

 which are requisite for its functions as a complete and independent nucleus, is 

 removed to make room for the supply of the necessary parts to it again by the 

 spermatic nucleus. ... I will venture to add the further suggestion that the 

 function of forming polar cells has been acquired by the ovum for the express 

 purpose of preventing parthenogenesis." To this it must now be pointed out 

 that so far as one polar globule is concerned, extrusion does not prevent 

 parthenogenesis. This view seems, according to Brooks, to have been first 

 advanced by M'Crady. It has been most carefully elaborated by Minot. 

 According to Minot, "in the cells proper, both sexes are potentially present; to 

 produce sexual elements the cell divides into its parts ; in the case of the egg- 

 cell, the male polar globules are cast off, leaving the female ovum." In 

 parthenogenetic ova, he supposes that enough male element is retained, since 

 only one polar globule appears to be formed. Van Beneden, whose opinion 

 is entitled to great weight, also inclines to regard the polar globules as male 

 extrusions. 



Sabatier distinguishes, besides true polar globules, other extrusions, and 

 believes the eliminated parts to be male elements. His views are connected 

 with an elaborate theory - of polarities, according to which, for instance, the 

 peripheral extrusions are male, while central cores (in the development of 

 sperms) are female residues. 



(6) A very different view — morphological rather than physiological — has 

 been maintained by Biitschli, Whitman, and others. The formation of polar 

 globules is an atavistic reminiscence of the primitive parthenogenesis. Just as 

 the mother sperm-cell or spermatogonium, which corresponds in the male to the 

 ovum in the female, divides up into what form spermatozoa, so the ovum retains 

 a slight power of division. Yet parthenogenetic ova, so far as polar globules 

 are concerned, show this least, nor can we well conceive an atavism so 

 universally present without some important physiological necessity directly 

 behind it. To Biitschli's view, however, such an authority as Hertwig inclines, 

 and Boveri likewise interprets the polar globules as "abortive ova." 



(r) Weismann's view is different from either of the above, though nearer the 

 first. He distinguishes in the nucleus of the ovum two kinds of plasma, — (i) the 

 ovogenetic or histogenetic substance, which enables the ovum to accumulate 

 yelk, secrete membranes, and the like ; and (2) the germ-plasma, which enables 

 the ovum to develop into an embryo. When the ovum is mature, the 

 ovogenetic substance has served its turn ; it is henceforth only an encumbrance ; 

 it is extruded as the first polar globule. This is all that is extruded in 

 parthenogenetic ova. The second extrusion is a reduction of the germ-plasma 

 itself by half, and the same must occur in the male germ-cell too. What is lost 



