32 DTJBLIN NATTTRAL HISTORY SOCIETY. 



more than one), and gives egress to separated portions of the endochrome, 

 individualized as zoospores, and not permitting it to extrude en masse 

 for the purpose of conjugating with the contents of a neighbouring frond ; 

 thus we not unfrequently observe in nature modifications of similar 

 means conducive to different ends. When the segment gives rise to one 

 tubercle only, this additional growth is gradually developed more and 

 more narrowly, diminishing to nothing at the opposite point of the cylin- 

 drical segment, so that the frond is thus thrown out of its straight or 

 nearly straight direction, and becomes bent into a knee-shape (Fig. 2). 

 Such is also the case when two such projections arise side by side. But 

 when two originate opposite to each other, or when there are three, 

 the frond is not thrown out of its straight form, because the new addi- 

 tion to the segment, from which these lateral growths take their origin, 

 now forms an annular extension equal all round, and the segment there- 

 fore becomes added to in length by just so much as the annular addition 

 is broad — and this is less than the 1 -3000th part of an inch (Fig. 4). As 

 the case is pretty similar whether there be one, two, or three of these 

 lateral growths, I shall continue my remarks upon those cases where one 

 only is formed. The basal tubercle now gradually elongates, and becomes 

 a tube in direct connexion and continuation with the frond (like the 

 finger to a glove), and is about 1 -3600th of an inch in diameter, but of 

 very varied degrees of length (Pig. 2). I have noticed some to cease to 

 grow after having barely attained about 1-1 0th or l-8th part of the 

 length of the frond, and I have seen a few very long, almost if not quite 

 as long as the frond itself. The endochrome near the base of each seg- 

 ment, and in the neighborirhood of the lateral tube, next becomes very 

 finely granular, of an almost homogeneous appearance and the lateral 

 tube is filled by it. The remainder of the endochrome (even in the state 

 indicated by Fig. 2) is still but little altered from the ordinary condition, 

 and the terminal cavities with the active granules, characteristic of this 

 genus as well as of Closterium remain unchanged. The annular addition 

 and the lateral tubes are quite smooth, and destitute of the scattered 

 puncta which characterize the empty frond in this species. 



Now it is, I apprehend, not a little worthy of remark that the 

 SAvarming, active, disintegrated granules disassociated from the rest of 

 the endochrome, described above as of frequent occurrence, are met with 

 at this stage, as well as frequently at the stage indicated by Fig. 1, when 

 the latei-al tube first appears as a mere tubercle ; and, moreover, presents 

 precisely the same appearance and conditions that other specimens of 

 this species {D. Elirenbergii) on the same slide exhibit, but which are not 

 destined to undergo the other changes here described. Further, nume- 

 rous other species, which occurred in the same gathering, presented si- 

 milar examples of the molecular swarming movement ; for example, 

 Docidium clavatum, Gonatozyon Ralfsii, various Cosmaria, &c. But I 

 think it is not less equally worthy of remark, that other specimens un- 

 dergoing the peculiar development, of which the production of the 

 lateral tube is a stage, did not indicate any molecular or swarming 

 movement of the minute granules of the endochrome — that in the termi- 



