270 THE MICROSCOPE. 



division of the mass takes place, and a number of pyriform 

 zoospores, each of which is furnished with a crown of cilise, 

 are set free. 



In many families of the olive-coloured Algae, reproduc- 

 tion by zoospores is the general rule ; they differ, however, 

 in the arrangement of their cilia. These organs, which 

 are always two in number, are usually of unequal length, 

 and emanate not from the beak, but from a reddish- 

 coloured point in its neighbourhood. The shortest is 

 directed backwards, and seems to serve during the motion 

 of the spoje as a rudder. The longest, directed forwards, is 

 closely applied to the colourless beak. Ectocarpus is one 

 of the simplest forms of olive-coloured Algae, consisting 

 of branching filaments, the extremity of any of which is 

 liable to become converted into a sporangium, by the ab- 

 sorption of the septa of the terminal cells. The zoospores 

 are arranged in regular horizontal layers. In many genera 

 a peculiarity exists, the signification of which is not yet 

 completely understood namely, that of a double fructifi- 

 cation. The ovoidal sporangia contain numerous zoospores. 

 In the genus Cutleria (fig. 150), there is seen another feature 

 of interest : the appearance of two kinds of organs, which 

 seem to be opposed to each other as regards their repro- 

 ductive functions. The sporangia not only differ from 

 those of other genera, but the frond consists of olive- 

 coloured irregularly-divided flabelli, on each side of which 

 tufts (sori) consisting of the reproductive organs, inter- 

 mixed with hair-like bodies, are scattered. The zoospores 

 are divided by transverse partitions into four cavities, each 

 of which is again bisected by a longitudinal median 

 septum. When first thrown oft' they are in appearance so 

 much like the spores of Puccinia, that they may be mis- 

 taken for them ; they are, however, about three times larger 

 than those of the other olive- coloured algae. 



The fruit of most olive-green Sea-weeds is enclosed 

 in spherical cavities under the epidermis of the frond, 

 termed conceptacles, and may be either male or female. 

 The zoids are bottle- shaped, each possessing a pair of cilia ; 

 the transparent vesicle in which they are contained is 

 itself inclosed in a second of similar form, and we have 

 no certain evidence of the function performed by the 



