128 



THALLOPHYTES. 



lorea). A number of hairs which grow in the receptacles among the sexual organs are 

 long, slender, articulated, but unbranched, and project in F. platycarpus out of the mouth 

 of the receptacle in the form of tufts (Fig. i6o, B). The Antheridia are produced as 

 lateral ramifications of branched hairs. Each antheridium consists of a thin-walled oval 

 cell, the protoplasm of which splits up into numerous small spermatozoids ; these are 

 pointed at one end, each furnished with two motile cilia ; in the interior they contain a 

 red point. The formation of the Oogonium begins with the papillose swelling of a 

 parietal cell of the receptacle ; the papilla is separated off by a septum, and divides, 

 as it grows in length, into two cells, a lower, the pedicel-cell, and an upper, which 

 forms the oogonium ; this swells up into a spherical or ellipsoidal form and becomes 

 filled with dark protoplasm. This protoplasm of the oogonium remains undivided in 

 some genera (Pycnophycus, Himanthalia, Gystoseira, Halidrys), and the whole contents 

 of the oogonium thus form an oosphere ; in others (Pelvetia) it splits into two, four 

 {0%othaUia imlgaris), or eight pieces (Fucus). Fertilisation takes place outside the recep- 



FlG. i6i.—Fua/s vesiailosus (after Thuret) ; A a branched hair bearinsj antheridia ; B spermatozoids ; / an oogonium, 

 Og^ after the contents have divided into eight portions (oospheres), surrounded by simple hairs (/) ; // commencement of the 

 escape of the oosphere ; the membrane (a) has burst ; the inner membrane i is ready to open (the two together constitute 

 an inner layer of the cell-wall of the oogonium ; /// oosphere surrounded by spermatozoids ; IV, V, gemiination of the 

 oospore (5X33o, all the rest Xi6o). 



tacles. The oospheres are expelled, surrounded by an inner membrane of the oogonium, 

 and escape through the opening of the receptacle ; the antheridia at the same time 

 become detached, and collect in numbers before the mouth of the receptacle when the 

 fertile branches are lying outside the water in moist air. When they again come into 

 contact with the sea-water, the antheridia open and allow the spermatozoids to escape, 

 the oospheres at the same time escaping from the envelope which still surrounds them, and 

 which is then seen to consist of two separated layers (Fig. i6i, 11). The spermatozoids 

 collect in numbers around the oospheres, become firmly attached to them, and when 

 their number is sufficiently great, their movement becomes so energetic that they impart 

 to the very large oosphere to which they are attached a rotatory motion which lasts for 

 about half an hour. Whether the spermatozoids force themselves into the oosphere 

 Thuret leaves undecided ; but analogy with the processes observed by Pringsheim in 

 Vaucheria and CEdogonium scarcely admits of a doubt that one or several of them mingle 

 their substance with that of the naked ball of protoplasm. A short time after these pro- 

 cesses are completed, the fertilised oosphere or oospore surrounds itself with a cell-wall, 

 fixes itself to some body or other, and begins, without any period of rest, to germinate, and, 



