PH.-EOSPOREAL 239 



ence is observable in size or form between those produced in the two 

 kinds of sporange, but those from the unilocular sporanges appear 

 in all cases to germinate directly, while those from the multilocular 

 sporanges are sometimes zoogametes with sexual functions. The two 

 kinds of sporange ma}^ be. borne on the same or on different indi- 

 viduals ; in the former case they are occasionally developed at different 

 times. In certain orders or groups one or the other kind is altogether 

 wanting. 



The various modes of sexual reproduction known in the Phc^ospore^e 

 present a most interesting gradual transition from the conjugation of 

 equivalent motile zoogametes to the impregnation of a quiescent 

 oosphere by motile antherozoids. In Ectocarpus (Lyng.), Giraudia (D. 

 and S.), and Scytosiphon (Ag.) conjugation takes place between swarm- 

 cells from the multilocular sporanges, which are to all appearance 

 exactly alike : but a slight sexual differentiation is exhibited in the fact 

 of one of them coming to rest and partially losing its cilia before conju- 

 gation takes place. In Cutleria (Grev.) and Zanardinia (Xard.) the 

 differentiation is more complete. The male and female swarm-cells are 

 produced either on the same or on different individuals : the latter are 

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

 their cilia before being impregnated by the former. In Dictyota (Lmx.) 

 the differentiation is carried still further, and the female reproductive 

 bodies are from the first motionless masses of protoplasm not provided 

 with cilia. In Dictyosiphon (Grev.) (Punctariacese) a different kind of 

 conjugation has been observed. 



The degree and mode of development of the thallus differ verv 

 widely within the class. A few species of Ectocarpaceae, belonging to 

 the genera Streblonema (Derb.) and Ectocarpus (Lyng.), are microscopic. 

 Some of the Mesogloeaceae and Ralfsiacese are small seaweeds epiphytic 

 on those of larger growth, with a flat radiating thallus reminding one of 

 Coleochcete. In some of the Ectocarpaceae the thallus consists of 

 simple branched or unbranched filaments resembling those of the 

 Confervaces. In the Sphacelariace^ each branch is composed of a 

 row of larger central surrounded by a layer of smaller cortical cells, all 

 originating from a large uncorticated apical cell. In the Cutleriaceae 

 filaments of cells become separated from the margin of the thallus, the 

 basal portions of which are coalescent into a sohd tissue, the increase in 

 breadth of which is due to the branching of the filaments. The 

 Laminariace^e include, in the genera Alaria (Grev.), Laminaria (Lmx.), 

 Macrocystis (Ag.), and others, the most gigantic of marine organisms, 

 in which the thallus or ' frond ' is to a certain extent differentiated 

 externally into rhizoid or organ of attachment, stipe or stem, and 



