ARCHER ON " PALMOGLCEAN" ALGM. 261 



experience, when I say that many — very many — of the assumed species 

 of Protophy ta and Protozoa are identical — the distinction on which their 

 separation has heretofore been based being entirely the result of the ac- 

 cidental conditions under which they have been reared. 



" In the Desmidiaceos, to which you direct attention more particu- 

 larly, it appears to me that such differences as the number of indenta- 

 tions, the acuteness or obtuseness of the teeth, the number of spinous 

 processes, and so forth, indicate mere accidental variations, handed 

 down, no doubt, from parent to progeny in the same locality so long as 

 the physical conditions remain the same ; but nevertheless not to be re- 

 garded as constant, or as impressed on the organisms ab initio as an inte- 

 gral feature in their physiological constitution. 



" It should be borne in mind that the onus probandi does not rest in 

 every example on those who think with me, but that it is quite suffi- 

 cient that we show a fair number of cases (as, for instance, in the genus 

 Micrasterias), in which unquestionable interchange of those characters 

 is to be met with, which by Ralfs and others have been seized upon as 

 indicative of distinct origin. For such cases prove that the law which 

 it is assumed governs the limits of species is no law, but only a condi- 

 tional direction, holding good only so long as the surrounding condi- 

 tions continue the same. 



" If, however, the object in view in defining varieties under spe- 

 cific designations is merely to render the identification of similar 

 forms more easy, I have nothing to say against it be}^ond this, that I 

 should be loth to have to make up the lists even as they stand now, and 

 firmly believe it will be an impossibility for the coming generation of 

 naturalists to do so at all." 



Mr. Archer said, he would for the present defer making any obser- 

 vations on the foregoing communication, inasmuch as he had added a 

 few remarks at the conclusion of the paper which he was just about to 

 lay before the Society, bearing on the questions put forward by Dr. Wal- 

 lich in the letter which he had just read. 



The following paper was then read : — 



Observations on the Genera Cylindrocystis (Meneghini), Meso- 

 t^nium (Nag.), and Spirot^enia (Breb.), (= Palmoglosa, Kutz. pro 



MAXIMA PARTE), MAINLY INDUCED BY A PAPER BY Dr. J. BrAXTON 



Hicks, P. R. S., P. L. S., on the Lower Porms oe Alg^:.* By 

 "William Archer. 



In a paper which I had the honour to read before this Society, in the 

 Session preceding last, on the Genus Palmoglcea (Kutz.),f I took the 



* " Remarks on Mr. Archer's Paper on Algse," in " Quarterly Journal of Microsco- 

 pical Science," N. S., vol. xii., p. 253. 



t "Proceedings of the Natural History Society of Dublin," vol. iv., p. 12; also 

 " Quarterly Journal of Microscopical Science," N. S., vol. iv., p. 109 (1864). 



