DUBLIN NATURAL HISTORY SOCIEXy. 71 



there is not the smallest difficulty in distinguishing them from any of 

 their allies. 'Now, analogy seems to me to be here an irresistible argu- 

 ment. Cosmarium Botri/tis, as some may maintain, only a variety of 

 Cosmarium margaritiferum, or of C. tctraopthahnum, or C. Brelissonii, &c. 

 — all of which they perhaps would lump together — reproduces itself from 

 the sporangium, conjugation being a true generative act, as I conceive. 

 My new Micrasterias differs by more salient and striking characters from 

 its nearest neighbouring forms than do those species of Cosmarium, 

 though it is to be mentioned that the development from the sporangium of 

 any species of Micrasterias is unknown. It is therefore reasonable to 

 conclude that my new Micrasterias and its allies are distinct species, as 

 they certainly are abundantly distinct forms. I consider, then, if certain 

 well defined, forms occur, dilferirig from their congeners as much as do 

 already acknowledged species, and which may be met with the very 

 next day by other observers, it is imperative that such be duly recorded 

 under a careful description. And I would remind you that this is the 

 necessary course in all departments of Natural History. Constantly re- 

 curring identical forms must be assumed to be the descendants of similar 

 progenitors, whatever be their intervening phases of development, of al- 

 ternation, or of metamorphosis ; and, as it seems to me, in the absence of 

 the various stages of the development of each from the germ generated 

 fi'om the parent, there is no more difficulty in believing such forms in 

 the microscopic world to be good species, than in the case of any of the 

 higher plants or animals, in the absence of tracing their growth from the 

 ovum or germ, though in one case we may possibly know the stages, and 

 in the other we may not. 



Therefore, on all these considerations, I believe I am not premature 

 in describing the following new species of Micrasterias ; and I make the 

 preceding few observations, and direct attention to the foregoing facts, 

 for the purpose of trying in, I fear, a very inadequate manner, to meet 

 the objections of those who seem to carry a prudent precaution as to 

 making new species too far, and thus, as it appears to me, to outstep 

 the truth in one direction, as much, or nearly so, as do those who over- 

 multiply species in the other. And those who may be disposed to 

 question the actual distinctness of certain of these Desmidian species, 

 and who ma}^ draw their arguments from figures or from preconceived 

 ideas, I would just beg to suspend their judgment until they make a 

 careful comparison of the living specimens side by side, drawn from dif- 

 ferent sources and on different occasions ; for I maintain that it is JN^ature 

 that should speak, and by JN'ature that we should be guided, and not by 

 opinion or theory, nor by any preconceived scheme, however ingeniously 

 devised, by which, after all, probably good species are unwittingly 

 grouped together into what are nothing but small subgenera (though, 

 without adopting that name, called indeed species),''the so-called varieties, 

 Nature compelling the distinctions at last to be acknowledged, being 

 the true species. I do not, however, mean to convey that I at all 

 imagine species to be invariable, and that authors, in disallowing certain 

 so-called species, in so doing always fall into the error I have alluded 



