i88 



entiation is more complete ; the male and female swarm-cells are pro- 

 duced either on the same or on different individuals ; the female are 

 much larger than the male, and come perfectly to rest, entirely losing 

 their cilia before being impregnated by the former. In the Dictyotacece 

 the differentiation is carried still further, and the female reproductive 

 bodies are from the first motionless oospheres not provided with cilia. 

 Several families of Phaeosporeae exhibit reduction or degradation of the 

 vegetative structure ; and among these we are disposed to place the 

 small group of Syngeneticce, consisting of but two genera, Hydrurus and 

 Chromophyton, which resemble one another in but few points except 

 the possession of a brown endochrome. In the former genus the pro- 

 pagative bodies are reduced to non-ciliated masses of brown protoplasm, 

 which germinate directly without impregnation ; in the latter the vegeta- 

 tive structure is almost entirely suppressed ; the propagative bodies are 

 uniciliated masses of protoplasm of two kinds, but without any observed 

 process of conjugation. The step from the Dictyotaceae to the FUCACE^E 

 is an easy one. In the highest type of brown seaweeds, such as Fucus or 

 Durvillasa, with their typical heterogamous or * oogamous ' reproduction, 

 consisting in the impregnation of a comparatively large oosphere by a 

 number of minute antherozoids, we have the highest attainment of this 

 series of development. 



The third line of descent from isogamous Confervoideae is a much 

 more direct one, to the CONFERVOIDEAE HETEROGAM.E, including the 

 three orders Sphceropleacece, CEdogoniacecE, and Coleoch&tacece. In the 

 first of these, which comprises only a single species, we have a distinct 

 differentiation of the male and female reproductive cells, the latter having 

 now become permanently quiescent ; but still a strong reminiscence of 

 the Confervaceae in the multinucleated cells. The CEdogoniaceae 

 exhibit a distinct advance in vegetative structure, and still more in the 

 cells which contain the male and female reproductive bodies being, for 

 the first time in this series, differentiated into antherids and oogones 

 respectively. Between the (Edogoniaceoe and the Coleochaetaceae we 

 have an evident connecting link in Bulbochsete ; but the typical genus 

 Coleochaete presents a singular reduction of the non-reproductive portion 

 of the thallus from a filament to a single plate of cells. The mode of 

 sexual reproduction has now attained a much higher degree of complexity. 

 The oogone is surmounted by a tubular appendage, the trichogyne, 

 through which the motile antherozoids find their wa.y to the oosphere 

 in order to impregnate it. The fertilised carpogone, as it is now called, 

 then becomes invested by a cortical layer of ceils, forming the complex 

 body known as the sporocarp. 



The Coleochaetaceae lead up .directly to the highest type of structure 

 attained by Algae, the FLORIDE^E or red seaweeds, a well-defined and 



