184 CYSTOSPERME^E. 



those cells, even in the young and but little developed Vesi- 

 culifera, which are destined to carry the true spores when 

 the species shall have arrived at the perfection of its life." 



Meyen, by whom this interesting structure seems first to 

 have 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, w T hich 

 the upper end of many of the joints of the Conferva repre- 

 sented exhibits. This appearance is altogether analogous to 

 the annular structure observed in the horny coat of the 

 Campanularice. In those polypi also this structure appears 

 first at an advanced period of growth, as is the case with 

 the Conferva, and indeed in very different species of articu- 

 lated plants of this family. The formation commences with 

 a thickening of the membrane; the constrictions then ap- 

 pear, which are not spiral, but run in horizontal rings one 

 above 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 with 

 my own observations. The structure is, amongst freshwater 

 Algae, confined to the species of the genus Vesiculifera. 



" The purpose to which the annular disposition of the horny 

 coat, of not merely the Campanularice but of most hydroid 

 Zoophytes, is subservient, is probably that of rendering their 

 polypidoms more flexible, and consequently less liable to 

 injury from the agitation of the restless element in which 

 they dwell." * 



The second particular refers to the central cytoblast or re- 

 productive vesicle, which, in the group of Cystospermece, is 

 circular, whilst in one genus of the Conjugatece, Zygnema, it 

 is somewhat quadriform, and furnished with tubular offsets. 



It is at once apparent, that the mode of reproduction just 

 indicated, does not differ essentially from that first made 

 known by Yaucher, with reference to the Conjugates, and 



* See Annals of Nat. Hist. 



