320 Causes and Course of Organic Evolution 



and allies a like disposition is seen, but the longitudinal bands 

 may branch, as they run over the periphery of the cell, a con- 

 dition well shown in Helminthocladia. 



When we pass to the marine genera, the chromatophore 

 becomes divided, and later on increased in number till many 

 small rounded or stellate masses result. Thus in the genus 

 Rhodochorton there may be two spirally wound chromatophores 

 in some species, or from 6-12 stellate ones in others, each 

 embedded in the peripheral protoplasm and bearing a large 

 pyrenoid center. In other of the marine genera, e. g., Ceramium 

 and Polysipho?iia, the several chromatophores may assume 

 diverse shape according to the size and position of the cell. 



In the development of reproductive organs a like evolu- 

 tionary advance is shoT\Ti from simple fresh-water to the most 

 specialized marine genera. Thus, if we start again with the 

 Chamsesiphonese, the genera Chamcesiphon, Radaisia, and 

 Hyella develop non-ciliate monospores from enlarged cells of 

 the thallus, as well as numerous and smaller conidiospores. 

 In Phragmonema, Goniotrichiim , and allies usually placed 

 with the red algse a similar origin of monospores occurs, but 

 sexual cell formation has hitherto not been observed, though 

 such may exist. In Rangia and allies monospores are formed 

 in a variety of ways, though all resemble fundamentally those 

 named above. But here sexual reproduction is also effected. 

 In this case cells that differ little from the spores, except that 

 they are much smaller, become physiologically differentiated 

 as spermatia or motionless male cells, while other cells of the 

 thallus that differ little from the vegetative cells, become 

 richly protoplasmic and evidently attract a spermatium by 

 energotactic action. The fertilized egg forms a 1-8 celled 

 spore-fruit that soon is liberated. 



In passing now through the simpler and mainly fresh-water 

 genera to those that are marine, a progressive complexity 

 alike in spermatial and egg production is observed, the main 

 stages of which are figured in the accompanying illustrations. 

 In Lemanea the spermatia vary from a few to a dense cluster 

 of surface cells, while in addition to the egg cell there are 2-10 

 accessory carpogone cells, the whole somewhat sunk in the 

 thallus. The fertilized egg produces loosely clustered chains 

 of carpospore or spore-fruit cells (Fig. 10). 



In Ratrachospennum and Chantransia there may, as in most 

 of the above, be monospores formed, and often in clustered 

 fashion. Or in some species of the latter genus tetraspores 

 arise by subdivision of a primitive monospore cell. The sex 

 cells consist of densely clustered spermatia and of clustered 



