230 ARCHER, ON DESMIDIACE^E. 



changing somewhat to an olive, finally turning brown, and 

 quite dying, and even, to a great extent, disappears (Figs. 3, 

 •1) . Each of the gonidia forming the external cluster appears 

 by this time to have formed for itself a special cell-wall of 

 slightly compressed or elliptic form, within which the green 

 contents may often be seen somewhat retracted. Now, a 

 movement within its circumscribed prison may be seen on 

 the part of the contents of a few of the gonidia, which takes 

 the appearance of a twisting motion, backwards and forwards 

 as it were, on its axis, similar to what may be sometimes 

 seen in the organisms called Trachelomonas by Ehrenberg. 

 I have not noticed them to turn completely round. These 

 gonidia are, however, greatly smaller, nor could I perceive 

 any red spot. If such a comparison might not appear wholly 

 out of place, I would be induced to say that the movement of 

 the green contents Avithin the confining membrane reminded 

 me somewhat of the movement of the eye in certain Ento- 

 mostraca. This movement is not apparent in all the whole 

 group of gonidia simultaneously, but only in a few at a time. 

 Eventually, one by one, the green contents leave the confining 

 membrane in which they have hitherto been detained ; but 

 my observation being here incomplete, and my avocations 

 calling me away, I am unable to say in what manner they 

 made their exit. There certainly appeared no neck-like 

 opening or perceptible aperture, but they probably emerged 

 by rupturing the boundary wall. Having, however, made 

 their escape, they swim away as ovate or pyriform ciliated 

 bodies, pale at the narrower or pointed end, and green other- 

 wise throughout — in point of fact, veritable motile gonidia, 

 or zoospores, in every way comparable to the similar bodies 

 found in other algae (Fig. 4); their principal distinction from 

 those, for instance, in Cladophora, being their temporarily 

 abiding in a cluster, each encysted in its special coating. I vainly 

 tried to satisfy myself whether these zoospores were one or 

 fivo-c'i\\a.ted, but I was not able to decide this difficult point. 

 They were about l-3600th of an inch in their narrower 

 diameter, and somewhat greater longitudinally. 1 Caving, one 

 by one, escaped, the vacated cells remain not Long attached 

 at the apex of the lateral tube, and I think they fall awaj t here- 

 from sometimes in a more or less connected condition, and 

 finally decay. The old frond now generally separates at the 

 suture, one segment bearing away the empty special struc- 

 ture described, the other, of course, unchanged ; any 

 remaining endochrome by this time being quite brown, 

 broken up, and dead, it' indeed it he not altogether vanished 

 (Fig. 4). I imagine it may be possible that in the native 



