314 Causes and Course of Organic Evolution 



While it is true that most of the genera and species have 

 now adopted an epiphytic or subparasitic habit, this may 

 merely indicate that by such artifice biologically they have 

 been able to survive, while many related genera of freer habit 

 may have succumbed. The family includes 17 fresh- water 

 genera with 86 species, and 6 salt-water genera with 8 species, 

 while 2 or 3 species are mainly brackish in habitat, a sufficient 

 indication that they originated as a group in fresh- water areas. 



They again exhibit close affinities with the Mycoidaceae 

 that consists of 5 genera and 10 species of fresh- water habitat, 

 and one genus %\'ith a single species of marine habitat. 



The Coleochsetacese is a family that has excited attention 

 during the past thirty years from its possible affinities with 

 the green algse on the one hand, and the bryophytic or even 

 pteridophytic groups on the other. These affinities were 

 connected Ts-ith the mode of growth of the thallus, the structure 

 of the green cells that compose it, the tendency in some to 

 formation of flattened expanses, and not least in the origin 

 and structure of the sex cells. In the structure of the thallus, 

 however, the family closely agrees also with some types of 

 the Chsetophoraceae and Mycoidacese. So forms that would 

 connect all three, and that might at the same time act as a 

 connecting bridge wdth bryophytic and pteridophytic groups, 

 were greatly desired. Such seems to exist in the fresh- water 

 genus Aphanochcete, that has been carefully studied by Huber 

 {98: 264). Formerly united Tsdth the Chaetophoracese, it is 

 now placed by Oltmanns {99: 240) in a separate family owing 

 to its interesting reproductive methods. For, while the Chse- 

 tophoracese mostly develop motile biciliate conjugating or 

 gamete cells of like size and appearance, in Aphanochcete they 

 are motile, tetraciliate, and of unequal size, the male cell or 

 spermatozoid being about a fourth to a sixth the size of the 

 egg cell. 



But it should be noted that Phceophila has been considered 

 to have similar tetraciliate gamete cells. Accepting it — as 

 can quite safely be done — that these and the other genera of 

 Chsetophoracese, as well as Coleochsetaceae, are a mere rem- 

 nant of abundant and allied genera, that once flourished so 

 far back as archsean times, they furnish collective evidence 

 that from the condition of motionless conidiospores, produced 

 in cells of the cyanophyceous Chamsesiphonacese, to the motile 

 biciliate or tetraciliate swarm cells of some Choetophoracea?, 

 from these again to biciliate or tetraciliate similar gamete 

 cells of most Cha?tophorace8e or of Phceophila^ from such to 

 biciliate or tetraciliate sperm cells and ciliate — as in Aphan- 



