ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 537 



truly an ovum, it is in many cases not completely so ; later eliminations 

 are often needed to complete the work. 



The diflfereut kinds of globules given ofi" from the egg-cell 

 between the time when it is an asexual cell and a complete ovum are 

 these : — 



1. Precocious globules which generally form follicular elements, 

 and which give, so to speak, the first imjiulse to the cell towards 

 a sexual condition. 



2. Globules which are more or less tardy in putting in an appearance, 

 and which may be formed some time before or only just before 

 maturity ; like the first, they arise by a simple differentiation in the 

 protoplasm, and not by karyokinesis ; they are the " globules tardifs " 

 properly so called. 



3. There are globules which are cotemporaneous with the period 

 of complete maturity, or the globules of perfect maturity. Most of 

 these are due to phenomena of cell-division, and they are the polar 

 globules properly so called. 



The author thinks that it is an error into which all embryologists 

 have fallen to regard the cellular nature of the polar globule as a 

 point of capital importance ; the principal, the necessary thing is the 

 expulsion of a mass of protoplasmic substance which represents the 

 male element ; it is only an accident that it is effected by a cellular 

 mode of segmentation. The essential fact is, in other words, the 

 completion of a sexual polarity. 



The lesson to be learnt from all the known facts may be thus 

 summed up : Their common and very general character proves them to 

 be of the highest value ; they all point to an elimination, or a ten- 

 dency to elimination, of a differentiated or undifferentiated portion 

 of the central protoplasm, and they show that the concomitant 

 phenomena are due to secondary circumstances which have no real 

 importance on the significance of the globules or of the substances 

 expelled by the egg. 



Considerable support, even if not categorical demonstration of the 

 validity of Sabatier's theory, is to be sought for in a comparative 

 study of the method of oogenesis in animals which are both sexually 

 and parthenogenetically reproductive ; if the theory is applicable to 

 the facts, we ought to find in parthenogenetic eggs either a complete 

 absence of, or a relatively small number of eliminated elements, the 

 number and presence of which in sexual cells ought, on the other 

 band, to be distinct and pronounced. 



What observations (as yet few in number) the author has made on 

 the history of the ova in Aphides seem to afford him the support he 

 needs ; still stronger support is given by Weismann's account of what 

 obtains in the Daphnoidea. 



In his historical survey Sabatier refers, of course, to the well- 

 known views of Balfour, and points out that that onibryologist looked 

 upon the portion of the germinal vesicle which tlie polar globule con- 

 tained as being the essential jifiint in the sexuality of the egg, and he 

 urges that the phenomena of karyokinesis are of no real importance ; 



Ser. 2.— Vol. TV. 2 O 



