184

CYSTOSPERMEiE.

those cells, even in the young and but little developed Vest-culifera, which are destined to carry the true spores whenthe species shall have arrived at the perfection of its life.”

Meyen, by whom this interesting structure seems first tohave been noticed, gives the following account of its charac-ters in a species which he calls Conferva rivularis: —

“ The annular structure appears worthy of notice, whichthe upper end of many of the joints of the Conferva repre-sented exhibits. This appearance is altogether analogous tothe annular structure observed in the horny coat of theCampanularia:. In those polypi also this structure appearsfirst at an advanced period of growth, as is the case withthe Conferva, and indeed in very different species of articu-lated plants of this family. The formation commences witha thickening of the membrane; the constrictions then ap-pear, which are not spiral, but run in horizontal rings oneabove the other. Sometimes it seems as if this ringed sub-stance were an entirely new formation.” — Meyen, Pflan-zen-physiologie, vol. iii. p. 451.

The above is the entire of Meyen’s account of this cor-rugated formation, which does not in all respects accord withmy own observations. The structure is, amongst freshwaterAlgas, confined to the species of the genus Vesiculifera.

“ The purpose to which the annular disposition of the hornycoat, of not merely the Campanularia; but of most hydroidZoophytes, is subservient, is probably that of rendering theirpolypidoms more flexible, and consequently less liable toinjury from the agitation of the restless element in whichthey dwell.” *

The second particular refers to the central cytoblast or re-productive vesicle, which, in the group of Cystospermem, iscircular, whilst in one genus of the Conjugates, Zygnema, itis somewhat quadriform, and furnished with tubular offsets.

It is at once apparent, that the mode of reproduction justindicated, does not differ essentially from that first madeknown by Vauchcr, with reference to the Conjugated :, and

See Annals of Nat. Ilist.