THE MOTILE ASEXUAL REPRODUCTIVE CELLS are spherical, egg- or pear-shaped, naked, _swarmspores_ (_zoospores_), which have arisen in other cells (_zoosporangia_), and propel themselves through the water by means of cilia; or they are _Phyto-Amœbæ_, which have no cilia and creep on a substratum by means of pseudopodia. The cilia, which are formed from the protoplasm (in the Bacteria, however, from the membrane), are mostly situated at the pointed and colourless end, which is directed forwards when in motion, and are 1, 2 (Fig. 5 _B_), 4 or more. Both the cilia in the Brown Algæ are attached to one side (Fig. 65); they are occasionally situated in a circle round the front end (_Œdogonium_, Fig. 6 _a_, and _Derbesia_), or are very numerous and situated in pairs distributed over a large part or nearly the whole of the zoospore (_Vaucheria_). Besides being provided with one or more nuclei (_Vaucheria_), they may also have a red “eye spot” and vacuoles, which are sometimes pulsating, _i.e._ they appear and reappear at certain intervals. The swarmspores move about in the water in irregular paths, and apparently quite voluntarily, revolving round their longer axes; but they come to the surface of the water in great numbers either because of their dependence on light, or driven by warm currents in the water, or attracted by some passing mass of food material. The swarmspores germinate, each forming a new plant, as their movement ceases they surround themselves with a cell-wall, grow, and then divide; in Fig. 6 _b_, two may be seen in the condition of germination, and about to attach themselves by means of the front end, which has been developed into haptera (see also Fig. 5 _B_, lowest figure). =The sexual reproduction= here, probably in all cases, consists in the coalescence of two masses of protoplasm, that is, in the fusion of their nuclei. [Illustration: FIG. 5.--_Cladophora glomerata. A_ The lower cells are full of swarmspores, whilst from the upper one the greater part have escaped through the aperture _m_. _B_ Free and germinating swarmspores.] [Illustration: FIG. 6.--_Œdogonium_: _a_ (free), _b_ germinating swarmspores.] [Illustration: FIG. 7.--_Zanardinia collaris. A_ Male gametangia (the small-celled) and female gametangia (large-celled). _C_ Female gamete. _D_ Male gamete. _B E_ Fertilisation. _F_ Zygote. _G_ Germinating zygote.]