MUSEUM OF COMPAKATIVE ZOOLOGY. 423 



In his criticism of Hertwig, Strasburger endeavors to show the impos- 

 sibihty of accepting the view that the germinative dot persists. Besides 

 the numerous results of other observers which seem irreconcilable with 

 it, a prime objection is, that it leaves no chance for the existence of polar 

 globules, which Biitschli and Fol have connected in their origin with 

 the germinative vesicle. One has only to assume that the half, and not 

 the whole, of Biitschli's spindle is ejected, the other half remaining in the 

 egg, in order to bring his own (Strasburger's) observations on the " canal 

 cells " of conifers into harmony with the results of Biitschli and Fol. 

 For Strasburger (loc. cit., pp. 293-297 and 18-21) makes the very 

 important discovery that in conifers the so-called canal cells present in 

 their formation points of resemblance to the polar globules of animal eggs. 

 After the cell nucleus has remained some time at the end of the egg 

 which is to receive the pollen tube, it is divided a short time before thi 

 fecundation into halves which are at once separated by a "Hautschicht- 

 platte." One half, which is accompanied by only a very small amount 

 of protoplasm, becomes the nucleus of the canal cell ; the other half 

 remains in the egg and in migrating from the pole leaves stretched 

 behind it fibres [interzonal filaments], which in turn disappear while 

 the nucleus, increasing in size, advances to the centre of the egg. This 

 is the " Eikern " (female pronucleus). The formerly expressed idea 

 that the canal cell is a rudimentary structure without recognizable 

 function is to be modified, inasmuch as it is the equivalent of the polar 

 globules, and by its formation the nucleus of Ihe primitive egg (Eian- 

 lage) frees itself of certain ingredients, and thus prepares for the ap- 

 proaching fructification. The protoplasm of the canal cell perishes 

 without function. He also finds the canal cell in Cycas. For mosses 

 and vascular cryptogams, however, only the " Bauchkanalzelle " is to be 



the cover. Having found the Jirst article, the existence of a second, which occurs 

 some pages farther on, was not suspected. 



Fol's description is limited to saying that the polar globules arise after the disap- 

 pearance of the germinative vesicle, and are produced by a process of cell division. 

 As this notice is not accompanied by figures, one is left without the means of 

 definitely confirming or rejecting the opinion I have expressed above about the 

 eggs studied by Strasburger ; the mere announcement, however, that polar globules 

 have been seen, only gives greater probability to my explanation. 



Since writing the above, I have been able to consult Stossich ('77, p. 225), and 

 find that he states, in a criticism of Rabl's theory of the significance of the polar 

 globules, that he has found these directive vesicles **in eggs of serpulas, ascidians, 

 and other animals subject to regular segmentation." This paper antedates that of 

 Fol by some three months, but does not contain any description especially devoted 

 to the formation of polar globules in the ascidians. 



