THE CENTROSOME AND THE BLEPHAROPLAST. 47 



arise de novo. They do not persist through several successive genera- 

 tions of cells, two cell-generations representing the maximum time of 

 their duration. In short, the blepharoplast develops merely the cilia 

 and forms, therefore, the locomotary apparatus of the spermatozoid. 



No phylogenetic relationship has as yet been shown to exist between 

 blepharoplast and centrosome. The fact is that, in those plants in 

 which blepharoplasts occur, there are no centrosomes with which to 

 show any phylogenetic relationship. The main reason, it seems, for 

 regarding the blepharoplast as the homolog of the centrosome is the 

 sole fact that the primordia of the former at a certain period of develop- 

 ment are provided with a system of radiations, giving them the appear- 

 ance of centrospheres. 



The view concerning the origin and phylogeny of the blepharoplast 

 as advanced by Strasburger is of interest, since it is the only one that 

 seems to take into consideration all the facts. Strasburger derives the 

 blepharoplast from the cilia-bearer of the zoospores and gametes in the 

 algae. In the zoospores of certain algse, e. g., Vaucheria, (Edogo- 

 nium, and others, the cilia spring from a localized thickening of the 

 plasma membrane (Hautschicht) at the anterior end. In CEdogonium 

 this kinoplasmic thickening is in the shape of a double convex lens, 

 from the edges of which arise the numerous cilia. In the large swarm 

 spore of Vaucheria the nuclei seem to be intimately connected with the 

 formation of the cilia-bearer. The nuclei migrate to the plasma mem- 

 brane and elongate in a direction at right angles to the surface of the 

 spore. The anterior end of each pear-shaped nucleus comes in contact 

 with the plasma membrane. That part of the plasma membrane in 

 contact with the nucleus thickens in the form of a delicate concavo- 

 convex lens, from two points of which, on opposite sides, spring the cilia. 

 The size and shape of the cilia-bearer vary, of course, in different 

 algae. Timberlake ('01) finds a small body at the base of the cilia in 

 Hydrodictyon, but it does not seem to be part of the plasma membrane. 



As Strasburger has pointed out, the " mouth-piece " of swarm spores 

 and gametes is not to be confounded with the cilia-bearer, since the 

 former represents the entire anterior end of the cell free from chloro- 

 phyll. It is true that the cilia-bearer is not well known in the sperma- 

 tozoids of algae, but transitions show that in all probability the sperma- 

 tozoids were derived from male gametes which in every way resembled 

 asexual swarm spores. The spermatozoids of Volvox globator are 

 regarded as a good illustration of this relation, for in structure they 

 occupy an intermediate position between the gametes of algae and the 

 spermatozoids of Chara. In Volvox the two laterally inserted cilia 

 would seem to indicate that the blepharoplast had undergone a lateral 



