252 Causes and Course of Organic Evolution 



brane. -On rupture of the membrane, the several swarmspores 

 are set free, each being provided with rarely one, usually two, 

 at times four, seldom numerous, cilia. From their ciliary 

 motility, these bodies have commonly been called zoospores, 

 and the mother-cells in which they have been formed zo- 

 osporangia. 



Such highly active and energized swarmspores may seem 

 to differ very widely from any condition seen amongst the 

 Blue-green Algae. But morphologically connecting stages 

 exist, we would consider. Thus amongst various of the Tetra- 

 sporacese the round or oval cells that are embedded in mucilage 

 bear elongated plasmatic processes that project through the 

 mucilage and into the surrounding medium. These have 

 been called pseudocilia by Correns; they are apparently mo- 

 tionless or slowly vibratile, and seem to be mainly tactile in 

 function. But end-cells in filaments of Oscillator ia described 

 by Phillips, and which have been watched for hours by the 

 writer, bear several slowly waving and rather blunt proto- 

 plasmic processes. So between the last and the active cilium 

 the main difference may be that the cilium is connected with 

 and largely energized by nuclear chromatin, as has definitely 

 been shown for some algoid cells and for spermatozoid cells 

 of the ferns and higher groups. 



We would therefore claim that the morphological connection 

 between blue-green and green algse now living is a close one, 

 when we compare certain groups of each. It is entirely ap- 

 propriate then to consider that many types which would once 

 have made the connection much more gradual and continuous 

 have been obliterated during past geologic periods. 



When we compare the behavior of the different kinds of 

 spore described above, the at times rapid transformation of 

 one into another is noteworthy. Thus in some genera of green 

 algae, such as Trentepohlia, Stigeocloniiim, and others, the 

 akinete cells may either grow into new individuals, or may form 

 a palmelloid stage, or advance instead to formation of swarm- 

 spores. So from examples such as these, and others already 

 indicated, we consider that the four modes of asexual spore 

 formation above described, can all be traced to have evolved 

 gradually from the Cyanophyceae upward; and that, with 

 completed evolution of the nuclear chromatin, originally pas- 

 sive non-ciliate (or possibly in forms now largely lost to us. 



