254 THE MICROSCOPE AND ITS REVELATIONS. 



The rapidity of the growth of this curious organism is not one of the* 

 least remarkable parts of its history. The individual cells of which the- 

 net is composed, at the time of their emersion as 'gonidia,' measure no* 

 more than l-2500th of an inch in length; but in the course of a few 

 hours, they grow to a length of from l-12th to l-3d of an inch. Nothing 

 has been as yet ascertained respecting the sexual Generation of this 

 type. 



252. Almost every pond and ditch contains some members of the 

 Family Confervacece ; but they are especially abundant in moving water; 

 and they constitute the greater part of those green threads which are to 

 be seen attached to stones, with their free ends floating in the direction 

 of the current, in every running stream, and upon almost every part of 

 the sea-shore, and which are commonly known under the name of * silk- 

 weeds/ or 'crow-silk.' Their form is usually very regular, each thread 

 being a long cylinder made up by the union of a single file of short cylin- 

 drical cells united to each other by their flattened extremities; sometimes 

 these threads give off lateral branches, which have the same structure. 

 The endochrome, though usually green, is occasionally of a brown or 

 purple hue; it is sometimes distributed uniformly throughout the cell 

 (as in Fig. 150), whilst in other instances it is arranged in a pattern of 

 some kind, as a network or spiral; but this may be only a transitory 

 stage in its development. The plants of this family are extremely favor- 

 able subjects for the study of the method of cell-multiplication by binary 

 subdivision. This process usually takes place only in the terminal cell; 

 and it may be almost always observed there in some one of its stages. 

 The first step is seen to be the subdivision of the endochrome, and the 

 inflexion of the ectoplasm around it (Fig. 150, A, #); and thus there is 

 gradually formed a sort of hour-glass contraction across the cavity of the 

 parent-cell, by which it is divided into two equal halves (B). The two 

 surfaces of the infolded utricle produce a double layer of cellulose-mem- 

 brane between them; this is not confined, however, to the contiguous, 

 surfaces of the young cells, but extends over the whole of their exterior, 

 so that the new septum becomes continuous with a new layer that is 

 formed throughout the interior of the cellulose wall of the original cell 

 (c). Sometimes, however, as in Conferva glomerata (a common species), 

 new cells may originate as branches from any part of the surface, by a 

 process of budding; which, notwithstanding its difference of mode, agrees 

 with that just described in its essential character, being the result of the 

 subdivision of the original cell. A certain portion of the ectoplasm seems 

 to undergo increased nutrition, for it is seen to project, carrying the 

 cellulose envelope before it, so as to form a little protuberance; and this 

 sometimes attains a considerable length, before any separation of its cavity 

 from that of the cell which gave origin to it begins to take place. This 

 separation is gradually effected, however, by the infolding of the ecto- 

 plasm, just as in the preceding case: and thus the endochrome of the 

 branch-cell becomes completely severed from that of the stock. The 

 branch then begins to elongate itself by the subdivision of its first-formed 

 cell; and this process may be repeated for a time in all the cells of the 

 filament, though it usually comes to be restricted at last to the terminal 

 cell. The Confervacew multiply themselves by zoospores, which are pro- 

 duced within their cells, and are then set free, just as in the Ulvacese 

 ( 246). 



253. A true sexual Generation has been observed in several Oonfer- 

 vaceae, and is probably universal throughout the group. It is presented 



