240 THE AMERICAN NATURALIST. [VOL. xxxix. 



other cytoplasm of the sperm at the end of the egg, passes 

 quickly to the center to unite with the female nucleus. The 

 blepharoplast remains near the periphery of the egg and may be 

 recognized even after the gamete nuclei have united. It finally 

 breaks down and its substance becomes lost in the cytoplasm of 

 the egg. The most complete account of the history of the ble- 

 pharoplast in the fertilized egg is that of Webber ( : o i ) . We 

 should naturally expect the first cleavage spindle in the cycads 

 and Ginkgo to be developed as in the conifers. Ikeno (:oi) 

 described clearly an intranuclear spindle in Ginkgo. In the 

 conifers, as previously described, the first cleavage spindle is 

 intranuclear and the fibers are developed freely from a mesh 

 and form a broad poled spindle without centrospheres. So that 

 not only does the blepharoplast break down at a distance from 

 the egg nucleus but we have no reason to think that there is 

 any place for a centrosome in the history of the first cleavage 

 spindle in the gymnosperms. 



We do not know clearly the fate of the blepharoplast in the 

 egg of any pteridophyte or bryophyte, although Shaw's (*98a) 

 studies on Onoclea indicate that it breaks down in the cyto- 

 plasm. Our knowledge of the thallophytes is equally incom- 

 plete as regards the history of the blepharoplast in the egg. 

 But both Strasburger ('97a) and Farmer and Williams ('98) 

 have agreed for Fucus that the two centrospheres at the poles 

 of the first cleavage spindle develop de novo and independently 

 of one another, and Williams (: O4b) holds the same view for the 

 centrosphere which appears at the side of the fertilized egg of 

 Dictyota. The sperms of the thallophytes are generally very 

 small cells and it may prove a difficult matter to follow their 

 blepharoplasts so that our opinions of events in these forms are 

 likely to be largely inferential from our knowledge in higher 

 groups. 



We can safely say that there is no evidence that the blepharo- 

 plast ever enters into the first cleavage spindle which is certainly 

 developed in the spermatophytes and probably in the pterido- 

 phytes without centrosomes or centrospheres. Where centro- 

 somes or centrospheres are known for the first cleavage spindle 

 in the thallophytes (Fucus and Dictyota), the observations indi- 



