4 INTRODUCTION. 



exact similarity of the contents of the different cells, no 

 difference being detected, even with the assistance of the most 

 powerful glasses, and the principal mode of growth of the 

 Conferva, by the extension and repeated sub-division of the 

 primary cell, would tend to lead likewise to a similar con- 

 clusion. 



Notwithstanding the difficulties which lie in the way of 

 regarding each cell of a Conferva as the representative of a 

 sex, the frequency with which the phenomenon of union of 

 the filaments, and commixture of the contents of two cells, 

 takes place, cannot be regarded otherwise than as most 

 curious, though the purpose to which it is subservient is so 

 obscure. It may be, that it merely serves to bring a number 

 of the reproductive granules into contact, and which, becoming 

 subsequently clothed with a membrane, are thus the better 

 preserved until the proper time for their germination arrives. 



Another circumstance opposed to the sexual view as re- 

 gards distinct cells, is that, in those genera even in which 

 either the cells or their contents unite, exceptions occur in 

 which there is an absence of conjugation of the filaments, 

 and commingling of endochrome or vesicular contents of the 

 cells ; and in other cases there is conjugation, but no mixture 

 of the endochrome of the united cells. 



Thus, so far as can be presumed, the information already 

 acquired would appear to be opposed to the belief in the 

 existence of sexes as applied to cells in the Conferva. A fer- 

 tilization of the sporules does doubtless occur ; and this I 

 believe to be effected through the agency of the following 

 structure, described, nearly as below, in the " Annals of Natural 

 History," vol. xii. p. 20. In this description it will be seen 

 that a double office has been attributed to it; I am now 

 induced to limit its use to the one, the important one, of 

 fertilization. 



From the high developement of the cells of many Alga, 

 both marine and freshwater, as well as from their extreme 

 transparency, in many species, it might have been supposed 

 that the first discovery of those curious organs, termed cyto- 

 blasts, which exercise an influence so mysterious on the de- 



