70 ARCHER AND DIXON, ON DESMIDIACE.E. 



there are occasionally found forms, as it Avere intermediate, 

 connecting them, it is assumed that these two original forms 

 must necessarily make but one species. On the other hand, 

 those naturalists might possibly be not wanting who would 

 1'ivl inclined to consider not only the two original, but also 

 one or several of those intermediate forms, as themselves 

 species. Both extremes, as it seems to me, may be wrong. 

 Might it not be expected to be the case that the limits of 

 variation of each of the two original species, so nearly allied, 

 might, so to speak, so touch each other at the margin, as to 

 seem to unite them together, and give rise to the assumption, 

 always plausible, but perhaps not always correct, that one of 

 the original species could (and does) , by a series of transitions, 

 pass into the other ? If any one species become modified, is 

 it not to be expected that the characters of the most nearly 

 allied form, and not those of one remote in affinity, will be 

 those which, to a greater or less degree, it will be likely to 

 simulate? Under this hypothesis, the two original forms 

 would still justly be considered true and distinct species — in 

 contradiction to the opinion of the former class of naturalists 

 — while the forms intermediate would be but variations 

 (perhaps but of a temporary or local nature), some derived 

 from one species, some perhaps from the other, and could by 

 no means be looked upon as true species — in opposition to 

 the views of the latter class of naturalists. I do not mean to 

 intimate, when a hitherto acknowledged species is rejected, 

 that I imagine the step always to be an erroneous one, for he 

 Avho successfully demolishes the spurious claims of a mere 

 book-species docs science a good service ; but it seems to me 

 that what I have tried to express is a state of things, the pos- 

 sibility of the existence of which, by those who arc anxious to 

 suppress species, may sometimes be lost sight of or ignored. 



There can be no doubt, however (and especially amongst 

 microscopic forms), that our lists are more or less encumbered 

 with the redundant names of false species, which further 

 research will doubtless eventually prove. Many forms which 

 now pass under distinct names may hereafter be found not 

 worthy to take specific rank in our By stems. And here it is 

 that the difficulty lies. In order to prove the identity of two 

 reputed species, over which there hangs a doubt, not only 

 must the happy opportunity be afforded of tracing the or- 

 ganism through its whole course of life, but, on the pari of 

 the observer, the requisite leisure and patient assiduity must 

 not be wanting. 



Nodoubl it is much easier to describe a new species than to 

 demonstrate that two, or perhaps more, familiar forms arc but 



