182 CYSTOSPERME.E. 



regular annulatlon of the enveloping membrane of the cells, 

 which would appear at a certain epoch to be intimately- 

 adherent to the tissue of the cells themselves. 



" The genus of freshwater Conferva which I have deno- 

 minated in a previous article Vesiculifcra^ , in addition to the 

 characters indicated in the definition of it given therein, such 

 as the attachment, attenuation and slight mucosity of the 

 filaments of the species composing it, as well as the formation 

 of true spores by the intermingling and union of the contents 

 of two cells in the same filament, is particularly distinguished 

 by the presence of a peculiar and regular annulatlon of the 

 enveloping membrane of the cells, which would appear at a 

 certain epoch to be Intimately adherent to the tissue of 

 the cells themselves." (PI. xvii. figs. 7, 8.) 



" This annular disposition of the sheath of the cells does not 

 occupy its whole extent, but corresponds only to certain cells 

 and determinate portions of those cells ; the cells around 

 which it is disposed being those in which the spores are 

 destined to be formed, and the portion of these which it in- 

 vests being the extremities through which no endochrome 

 passes from the contiguous cells for the formation of the true 

 spores, or rather perhaps sporangia. 



" The number of annuli which correspond to each fructi- 

 ferous cell varies according to the species, and is more consi- 

 derable in the long-celled species ; it would appear however to 

 be never less than two, or more than eight or ten, to each cell. 



"The use of this interesting structure is much more apparent 

 than that of the provision already noticed as belonging to one 

 section of the genus Zygnema, and admits of a most satis- 

 factory explanation, it being manifestly designed to aflfbrd an 

 outlet to the imprisoned spores, which it may be supposed to do 

 in the following way. As soon as the species has reached its 

 maturity and the spores have become perfected, the annuli, 

 Avhich are intimately united to the cells, contract, most pro- 

 bably from the arrest of growth and diminution of vitality 



* This genus was first established by me in the " Annals and JNIaga- 

 zine of Natural History," vol. x. p. 385. ; it will be seen, however, that 

 the views here expressed differ in many respects from those therein stated. 



