30 Mr. A. Hassall on the Fresliv)ater 



production, situated at one side of the distal extremity of each cell ; 

 in the Conjugating tribe the zoospores pass out through the open- 

 ings of the connecting tubes of the cells, which, when reproduction 

 has been completed, separate from each other ; and lastly, in the 

 Vesiculiferce, as has been shown, a more complicated provision ex- 

 ists for the egress of the spores and zoospores. 



Of all characters whereljy the Vesiculiferce may be distinguished 

 from other Confervfe, that derived from the conjugation of the in- 

 vesting sheath is perhaps the most valuable, from the circumstance 

 not merely of its being confined to the species of that genus, but 

 from its constant presence in ail stages of their development ; 

 and not only is it interesting as being indicative of a Vesicidifera, 

 but also as pointing out those cells, even in the yoimg and but 

 little developed Vesiculifera, 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 characters in a 

 species which he calls Conferva rivularis : — 



" The annular structure appears worthy of notice, which the 

 upper end of many of the joints of the Conferva represented ex- 

 hibits. This appearance is altogether analogous to the annular 

 structure observed in the horny coat of the Campanularice. In 

 those poljioi also this structure appears first at an advanced period 

 of growth, as is the case ^dth the Conferva, and indeed in very 

 different species of articulated plants of this family. The forma- 

 tion commences with a thickening of the membrane ; the con- 

 strictions then appear, which are not spiral, but run in horizontal 

 rings one above the other. Sometimes it seems as if this ringed 

 substance were an entirely new formation." — Meyen, ' Pflanzen- 

 physiologie,' vol. iii. p. 451. 



The above is the entire of Meyen's account of this corrugated 

 formation, which does not in all respects accord with my o'mi ob- 

 servations. The structui'e is, amongst freshwater Algae, confined 

 to the species of the genus Vesiculifei-a. 



The purpose to which the annular disposition of the horny coat, 

 of not merely the Campanularm but of most hydroid Zoophytes, 

 is subser\'ient, is probably that of rendering their poh^idoms 

 more flexible, and consequently less liable to injury from the 

 agitation of the restless element in which they dwell. 



I have, in conclusion, to record my thanks to the Rev. M. J. 

 Berkeley for the friendly interest which that gentleman has taken 

 in the above observations, as well as for the valuable references 

 and extracts from the ' Flora,' &c. incorporated with these remarks. 



Cheslmnt, May 14, 1843. 



