IY. 
EUCACEflA 
51 
branches or leaves, which then become succulent and full of slimy mucus ; and in 
the highest types, small metamorphosed branchlets are from the beginning set apart 
as organs of fructification. These metamorphosed branchlets, or the swollen parts 
of ordinary branches which are filled with spore-cavities, are called receptacles ; 
( receptacula , Ag. — Endl. — carpomata, Kiitz.) 
Each spore cavity , placed immediately beneath the outer wall of the frond, and 
communicating freely with the water through its pore, is a hollow, spherical, 
membranous, bag-like chamber, whose inner surface is clothed with pellucid hairs 
(paranemata), among which organs of fructification of two kinds (male? and 
female) are placed. Sometimes both kinds or sexes are found in the same cavity ; 
sometimes all the cavities of one plant produce one kind only, and all those of 
another plant the other kind. (A vertical section of one of the female spore-cavities 
of Fucus furcatus , figured at our Plate III. A, fig. 4, will show the general appear- 
ance of the fructification.) 
The spores are lodged within colourless, glassy perispores , or large, swollen, 
membranous, closed cells, attached to the walls of the cavity ; each perispore 
containing from one to eight, and most commonly four spores. The perispore 
originates, like the hairs or paranemata, from the wall of the cavity, and appears 
to be formed from one of these hairs, which, having been fertilized at an early 
period of its development, instead of continuing to grow by the production of new 
cells at its apex, like an ordinary hair, has been arrested at the first or second cell ; 
and this cell, becoming enlarged, has an endochrome gradually elaborated within 
it, and finally either condensed into a single spore or divided into several. In an 
early stage the colouring matter, or endochrome, is of a very fluid substance, and 
pale olive hue. Gradually it becomes darker and more opaque, its particles lying 
closer together, and at length is partially solidified and invested with a delicate 
membranous envelope, which constitutes the testa of the spore. In Halidrys , 
Cystoseira , and several other genera, each perispore contains at maturity but a 
single spore ; in Fucus and others, the number of spores varies from two to eight, 
or perhaps a larger number. 
The paranemata are either simple or branched. Those which produce Anther idia 
are always branched, and the antheridia are formed from the terminal cell of each 
branchlet, which is enlarged and ovate, obovate, or club-shaped. This Antheridium , 
or supposed male, is a pellucid, enlarged, closed cell, containing a multitude of 
minute corpuscles ( sporidia , Ag.), which are supposed to represent the pollen, if not 
to fulfil its office in fertilizing the spore. They are oval, somewhat pointed at one 
end, and contain a reddish-orange granule ; and they are furnished with two 
extremely slender vibratile hairs or cilia , one of which issues from the narrow 
extremity of the corpuscle ; the other, which is of greater length, from the coloured 
granule. The corpuscles, at first contained within the antheridium, at length issue 
from it, escaping into the surrounding water, and immediately commence a suc- 
cession of rapid movements to and fro, and in circles and curved lines, strikingly 
similar to the ciliary movements of some of the Infusoria, or of the spores of 
some of the fresh water Algae of the Green series. These movements depend on 
the rapid vibrations of the cilia. During progression, the narrow end of the cor- 
