8. With the organs last described we think we need have little hesitation in comparing the structures to which the same name has been applied, as they occur in the Fucacem. The fructification of these plants is, as is well known, enclosed in spherical cavities, situate under the epidermis of the frond, which are called conceptacles, and may be male, female, or hermaphrodite, according to the organs which they contain. The male concepta cies present in their interior an arrangement of branched filaments, or hair-like organs, which, taking their origin from the surrounding cellular tissue, converge towards the pore. At the summits of these filaments, the so called antheridia are supported, which consist of little ovoid transparent vesicles. They contain, in their early condition, a granular protoplasmic material, but as they approach maturity, the so-called antherozoids make their appearance. These last are hyaline corpuscles, not exceeding about thz- of an inch in their longest dimension. Each con tains a granule of a greyish or reddish orange colour, from which the organs of locomotion emanate. The form of the zoids differs ac cording to thegenns. In Fucus, they are bottle shaped, and each possesses a pair of cilia, one of which, the shortest, is directed forwards from the neck, while the longest emanates from the coloured point and is pointed back ards. In Halidrys, the zoid is ovoid or spherical, and the longest cilium is directed forwards. In Fucus and several other genera, the transparent vesicle in which the zoids are immediately contained, is itself enclosed in a second of similar form. At the period of maturity this last gives way at its apex: the internal sack is expelled, and at once finds its way towards the external opening. In the meantime its delicate membrane disap pears, and the liberated zoids commence their active motions.
9. Although the antherozoids of the Fu coidex differ from the zoospores of the other olive-coloured Algw, in their not possessing the power of germination, there are yet remarkable points of correspondence between them, in their form, structure, and mode of develop ment. Both are composed of a hyaline pro toplasma, and the position of the coloured granule, as well as the arrangement of the cilia, corresponds. They differ, in the first place, in size, and secondly, in respect of the chloro phylle granules, which are present in the zo ospore, but absent in the antherozoid. As regards the question of their functional sig nification, they may be considered, on the one hand, as the elements of a male secretion, and the organs in which they are contained, as antheridia ; on the other, we may look upon them as the formal representatives of structures destined in other families to the performance of functions of which they are themselves incapable. In favour of the first of these views we have no direct evi dence, and must trust entirely to analogy. We know that in Cutleria and its allies, the zoospores display the power of germi nating without the slightest reference to the presence or absence of the secretion of the supposed male organ. Further, if, as all obser vations which have been hitherto made, tend to prove, the zoospores of all the green Algx, and of so many of the olive-coloured, normally germinate undet the condition of the constant non-existence of such organs, it is difficult to see why an exception should be made in favour of those of other families in which they are present. As regards the Fucoidete, we have certainly no evidence whatever that the antheridia perforin any. function, either more or less important in the reproductive process.
10. In the family of Vaucheriacem, the zoo sporous reproduction is remarkably modified by the substitution of a single multiple zoospore, of large size, for a number of smaller ones. The frond of Vaucheria consists of a branched tube, and much resembles in general form, that of the Bryopsidex, from which the Vau cherix in their vegetative condition differ only in respect of the arrangement of the chloro phylle. The commencement of the formation
of zoospores is announced by the condensa tion of the green protoplasma in the rounded terminations of the branches of the plant. This condensation is accompanied with an enlargement of the cylindrical filament, which soon appears club-shaped, and is completely occupied by a confused and opaque dark-green mass. Shortly afterwards a septum is formed, which limits the terminal portion of the tube. Within the separate cavity thus formed, the mass of protoplasma becomes further con densed; its margin being surrounded by a clear space which intervenes between its external sur face and the tube membrane. This body, which possesses an oval form, is the future zoospore. No sooner is it completely developed than the membrane which encloses it gives way at the apex, and it begins to insinuate itself through the resulting narrow opening. Having com pletely freed itself, it forthwith commences an active progressive motion, which is accom panied by a circumvolution round its axis. The zoospore at this period possesses no dis tinct or consistent investing membrane, as is evident from the fact, that if, during its escape, it divides accidentally into two —a circum stance which not unfrequently happens, from the relative narrowness of the opening through which it has to pass —each part is complete in itself and capable of germination. Its whole surface is covered with vibratile cilia, which are apparently connected with an epithelium like structure. In this arrangement there seems to be an indication of a tendency to a division into smaller particles, by the melting together of a Dumber of which the whole may be conceived to be formed. Like all zo ospores its period of active motion is short; it soon becomes stationary and begins to germi nate.* The zoospores of Vaucheria seem to correspond closely with the motionless spores of the true Dictyotace (Dictyota, Padina, &c.), as well as with those of the Fucacew. In the case of the latter, the accuracy with which their structure and germination have been studied, has enabled us to follow out the analog,y more closely. In speaking of the an theridia (§ S.), we described the general form of the conceptacles. In the moncecious and dicecious Fuci, the female conceptacles are distinguished from the male by their olive colour. The spores are developed each in the interior of a perispore, which is borne on a pedicle emanating from the inner wall of the conceptacle. They make their escape by the rupture of the perispore at its apex. At the moment at which this takes place, the spore is perfectly simple, except that in one or two species the surface is covered with cilia, which seem to resemble those of Vaucheria. Soon afterwards, a remarkable series of changes occurs, consisting in the splitting of the en dochrome into a number of masses —usually eight —each of which becomes isolated, and finally assumes the form of a smooth and spheroidal sporule, provided with an investing membrane. About twenty-four hours after the completion of this process, germination com mences. It consists in the budding out of the membrane of each sporule, at some point of its surface, into a nipple-shaped projection, which in the following forty-eight hours, elon gates into a cylindrical tube; shortly afterwards the whole body of the sporule is converted by repeated division into a mass of cells, in which condition it has been by many writers mis taken for the original spore, and described as such. The Vaucheriw present the peculiarity of a double mode of reproduction. In the earlier periods of the growth of the plant, there occurs the successive formation of aggre gate zoospores of large size at the termination of the branches, as above described. In the older fronds these are no longer observed, their place being taken by organs producing germs which are capable of retaining for a long period their power of development.