Io6 THE EVOLUTION OF SEX. 



§ 9. Theories of the Polar Globules. — The polar globules appear to 

 have been first observed in 1848 by Fr. Miiller and Loven, but it is only 

 within recent years that much has been made of them. Thanks to the 

 masterly researches of Butschli and Hertwig, Giard, Fol, and others, it 

 became possible to interpret the extrusion as a case of cell-division or 

 budding. More recently, Van Beneden, whose monograph on the ovum of 

 the threadworm {Ascaris) will remain one of the classics in this department 

 of research, has raised a protest against regarding the extrusion as a 

 normal cell-division. The details of the 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 of 

 " 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 ex- 

 pressed 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 neces- 

 sary 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 con- 

 cerned, 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 

 glol)ules 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. 



(/<) 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 fhr as polar-globules are concerned, show this least, nor can we well 

 conceive an atavism so universally jiresent without some important physio- 

 logical necessity directly behind it. To liiitschli's view, however, such an 

 authority as Hertwig inclines, and Boveri likewise interjirets the polar 

 globules as " abortive ova." 



