CRITICISMS AND CONCLUSIONS. 65 



rounding fluid in the oviduct or follicle and by the tissues of the oviduct 

 or ovary. Kirkham, furthermore, states that this loss of the polar cells 

 occurs during ovulation; but, since he has not seen any instances in which 

 the eggs are passing from the follicles, this conclusion must be based on 

 the presence of these bodies at one stage (viz, before ovulation) and their 

 absence at another (viz, after ovulation). But, unfortunately for this 

 explanation, they are not universally absent in the latter case. 



None of the figures of mammalian eggs escaping from the follicle 

 the only ones known to us being those given by Barry (1839), Sobotta 

 (1895), van der Stricht (1901), and the writers (figs. 38, 39, 40) furnishes 

 any evidence whatever that the polar cell is being pressed through the 

 zona pellucida. Our preparations show, on the contrary, an increased 

 space between the zona pellucida and the vitellus. The change in osmotic 

 conditions in passing from the ovary to the periovarial space or to the 

 oviduct in a living mouse can scarcely be great enough to cause the 

 polar cell to be forced through the zona by shrinkage of the latter. 

 Furthermore, if the loss of the first polar cell is caused by the action of 

 reagents, why should not the second polar cell also be forced through 

 the zona? In the case of the bat van der Stricht had the evidence of 

 both polar cells lying outside the zona. There is not even this evidence 

 in the case of the mouse, for, as Sobotta (1908, p. 253) has observed, no 

 one has ever seen such a condition, though, if it occurs, the polar cells 

 should be easily recognizable among the surrounding follicle cells. 



There is, then, no good evidence of the suppression of either polar 

 cell or of the loss of the first polar cell by extrusion through the zona 

 pellucida. Lams et Doorme (1907, pp. 276, 287) were the first to offer 

 the explanation that, while both polar cells are formed, the first under- 

 goes degeneration within the zona and disappears. Their figures show 

 this clearly, yet they suggest that what they call degenerating polar 

 cells may possibly be bodies (follicular cells) which have slipped under 

 the zona! Independently of Lams et Doorme, and before their paper 

 was published, we, also, had come to the conclusion that the first polar 

 cell degenerates, and can therefore support the view with unbiased 

 observations. We have already described the decrease in size of the first 

 polar cell and the evidence of the degeneration of its chromatin, using 

 polar cells of eggs which contain the second spindle in order to avoid 

 even the possibility of confusing the first polar cell with the second. 

 Tafani (1889, p. 24) mentions that the first polar cells vary in size and 

 also calls attention to cases where they are very small. Sobotta (1907, p. 

 544) alludes to these small forms by warning his readers not to mistake 

 for polar cells what he says may be follicle cells under the zona, or bodies 

 formed from the zona. He does not show why follicle cells should be 

 under the zona, or in what manner they could get into such a position, 

 or how the zona could give rise to bodies with nuclei. It must be remem- 

 bered that, since Sobotta's material contained a large proportion of the 



