170 NATURAL HISTORY SOCIETY OF DUBLIN. 



that its motions are assisted by the cilia ; but they have not yet begun to 

 play, nor, if they had, could they cause that alteration of figure, "like 

 that of a Euglena, from second to second," of which Cohn speaks.* 

 There can, I think, be no doubt but that the zoospore here, in such ac- 

 cidentally difficult cases, is mainly assisted in its birth by its own 

 innate contractility. Nageli,f and, apparently following him, Vaupell, % 

 seem to urge that an exosmotic action operates upon the young zoospore, 

 inducing the phenomena described. Cohn likewise, § in such cases 

 (speaking of the zoospores of Vaucheria and Hydrodictyon), where the so- 

 called primordial utricle (outer protoplasmic layer) presents contrac- 

 tions and expansions, seems to have arrived at the conclusion that such 

 alterations of figure are wholly due to the taking up and withdrawal of 

 water, and not to any special inherent contractility. The very interest- 

 ing experiments upon Spirogyra, Closterium, &c, which Cohn describes 

 seem to prove only that by the alternate absorption and withdrawal of 

 water the cell-contents become contracted or expanded as a whole, that 

 is, become alternately changed in bulk and density ; but it does not to 

 me appear that such experiments call forth anything like " rhizopo- 

 dous" phenomena, such as those described in this Paper, nor will the 

 results of such experiments account for them. The former (that is, auto- 

 matic contractility) is, I venture to believe, far more likely to be the true 

 solution. Many other similar instances in zoospores (for instance, Vau- 

 cheria), as is well known, might be here cited. Yet in his elaborate 

 memoir on Protococcus pluvialis (Kiitz.), || published previously, the latter 

 observer seems to dwell upon the similarity of the contractile pheno- 

 mena presented by the primordial utricle of that remarkable organism 

 to those shown by Euglena and Astasia ; and he bases thereupon cer- 

 tain comparisons of the vegetable protoplasm to that of the animal, lead- 

 ing him to the conclusion that these are quite analogous, correctly 

 regarding (as I conceive) Protococcus pluvialis as a plant, and assuming 

 Euglena to be an animal. However, his own very interesting observa- 

 tions on Euglena,** as well as those of others, seem rather to point to 

 the conclusion that this puzzling organism is really a phase of a plant. 

 Hence, as I conceive, it seems to have needed such observations as those 

 of Dr. Hicks, and that on Stephanosphsera here recorded — that is to say, 

 evidence of automatic rhizopodous movements in undoubted plants — to 

 complete the proof of the similarity of the animal and vegetable proto- 

 plasm. 



Again, in our search for analogous cases, as regards cells which are 

 not zoospores, let us refer to the figures of my Mesotanium mirificum, 



* Loc. cit. (" Untersuchungen uber d. mikr. Alg. u. Pilze"), p. 231. 

 f " Pflanzenphysiologische Untersuchungen." 

 X Loc. cit. (" Iagttagelser," &c), p. 29. 



§ Loc. cit. ("Untersuchungen liber d. mikr. Alg. uud Pilze"), pp. 228, 230. 

 || "Znr Naturgeschichte des Protococcus pluvialis (Kiitz.)." In abstract, in Ray- 

 Society's Publication for 1853. 

 ** Ibid., p. 733. 



