[18] Carbonnier. “L’Écrevisse,” p. 8.
In Germany, the two forms have long been popularly distinguished, the former by the name of “Steinkrebs,” {290} or “stone crayfish,” and the latter by that of “Edelkrebs,” or “noble crayfish.”
Milne Edwards, it will be observed, speaks of these two forms of crayfish as “varieties” of the species Astacus fluviatilis; but, even as far back as the year 1803 some zoologists began to regard the “stone crayfish” as a distinct species, to which Schrank applied the name of Astacus torrentium, while the “noble crayfish” remained in possession of the old denomination, Astacus fluviatilis; and, subsequently, various forms of “stone-crayfishes” have been further distinguished as the species Astacus saxatilis, A. tristis, A. pallipes, A. fontinalis, &c. On the other hand, Dr. Gerstfeldt,[19] who has devoted especial attention to the question, denies that these are anything more than varieties of one species; but he holds this and Milne Edwards’s “second variety” to be specifically distinct from one another.
[19] “Ueber die Flusskrebse Europas.” Mém. de l’Acad. de St. Petersburg, 1859.
We thus find ourselves in the presence of three views respecting the English and French crayfishes.
1. They are all varieties of one species—A. fluviatilis.
2. There are two species—A. fluviatilis, and A. torrentium, of which last there are several varieties.
3. There are, at fewest, five or six distinct species.
Before adopting the one or the other of these views, it is necessary to form a definite conception of the meaning of the terms “species” and “variety.” {291}
The word “species” in Biology has two significations; the one based upon morphological, the other upon physiological considerations.