48 INTRODUCTION. 



displacement, for the entire anterior end of the spermatozoid of Volvox 

 is certainly not blepharoplast. (The very suggestive theory of Stras- 

 burger carries with it a certain degree of probability, yet to what extent 

 it is true further research must determine.) 



If, however, any genetic relationship exists between centrosome and 

 blepharoplast, the evidence is certainly to be sought in the lower 

 plants. In this connection it is of the greatest importance to know 

 first of all whether, in such algae as the Sphacelariacece, in which 

 centrosomes are known, any relation exists between the centrosome 

 and cilia-bearer, assuming, of course, that the cilia arise here also from 

 a differentiated body. In Chara and in those Archegoniatcs^ with 

 blepharoplasts no centrosomes are found, neither is any such body 

 known to take part in the formation of the spindle in such algas as 

 (Edogonium, and others in which highly developed cilia-bearers 

 occur. Although these facts do not prove anything, yet they lend 

 encouragement to the belief that centrosome and blepharoplast may be 

 homologous structures, or in some degree phylogenetically related. 



Those who maintain that the cilia-bearers are centrosomes have not, 

 it seems, approached the question from the standpoint just mentioned, 

 but seem to have based their conclusion upon the resemblance between 

 blepharoplast primordia and centrospheres, or upon analogies between 

 the spermatozoids in plants and the spermatozoa of certain animals. 



Belajeff ('99), who claims that blepharoplasts are homologous with 

 centrosomes, strengthens his view by his observations in spermagenous 

 cells of Marsilia. In the grandmother-cells of the spermatozoids of 

 this plant he finds that the blepharoplast primordia, which lie some 

 distance from the nucleus, divide previous to the division of the nucleus, 

 and between the two separating daughter primordia a small central 

 spindle is developed just as in certain animal cells. From this small 

 amphiaster the karyokinetic figure is developed. This, if true, is the 

 first case on record in plants in which a central spindle is formed 

 between the daughter centrosomes, lying in the cytoplasm some dis- 

 tance removed from the nucleus. 



In the light of what is now known concerning the development of 

 the spindle in Chara and in the Pteridophyta, the author entertains 

 serious doubts concerning the accuracy of Belajeff's statement. Oster- 

 hout's ('97) studies on the development of the spindle in the spore 

 mother-cells of Equisetum prove beyond all question that centrosomes 

 are not present in that genus. In other Pteridophyta the majority of 

 all investigations, which have been thorough or reasonably exhaustive, 

 shows that centrosomes or centrospheres are absent there also. 



1 Ma.rcha.ntia. polyntorpha excepted. 



