10 INTRODUCTION. 



central organ are really sometimes more than mere streams ; 

 at least, that they are mucous threads, since they become 

 tinged brown with the tincture of iodine, and do not in the 

 least alter either their form or position. Schleiden has also, 

 at the same time, observed reticulate, anastamosing little 

 streams upon the central wall of the cell, but especially at 

 the free ends where the green spiral bands cease, and the 

 cells consequently become lighter and more transparent. 

 This appearance, also, has not yet presented itself to me. J 

 have, however, more than ten years ago, seen in the Zygne- 

 mata, motions of very little granules, which resemble those 

 which I have already pointed out in Oedogonium vesicatum 

 and O. capillare. They extend sometimes throughout the 

 entire inner space of the cell, and are especially evident in 

 freshly broken-off terminal cells. That the cytoblast really 

 occasions this motion, I doubt, because it occurs in all 

 the other cells of the Alga which do not possess the central 

 organs." 



Having thus described what I conceive to be the organ 

 whereby the reproductive germs are fertilized, we come now 

 to consider these bodies themselves, which, according to 

 some observers, are twofold zoospores and spores. We shall 

 speak first of the former. When a portion of a Conferva, 

 for example a Vesiculifera, in an early condition of its growth 

 is placed beneath the microscope, in each cell are observed 

 numerous spherical granules, each having a dark central 

 nucleus, and the size and amount of these varying ex- 

 tremely ; and all being, at this period, connected with each 

 other by a tubular or vascular network.* As the species ap- 

 proaches to a state of maturity, these bodies will be seen to 

 have undergone a considerable increase of size and change of 

 form, they now being no longer spherical, but pyriform, the 

 inflated portions being filled with endochrome, in the midst of 

 which one or two incipient germs can, even at this early 

 period, be observed, and the apices, or, as they have been 



* For an account of this, see paper by me in " Annuls and Magazine 

 of Natural History," vol. xii. p. 25. 



