198 L. A. BORRADAILE. 
(a) Let us suppose the environment to alter. Its effect upon a varietal species might 
take one of several forms: (i) It might affect all varieties equally, either favourably, un- 
favourably, or not at all. (ii) It might extinguish all but one. In either of these events 
the species as a whole would change its characters, but there would be no transformation 
of a group of varieties into a group of species. (a1) In a species with three or more 
varieties, in which the extreme varieties are connected (structurally, not necessarily genetically) 
by intermediate varieties, it might extinguish the intermediate variety or varieties, leaving 
the extreme ones as separate species. (iv) In a species with two or more varieties, it 
might affect all or some of the varieties favourably in their most marked form and _ prove 
prejudicial to the intermediate individuals between the varieties. By this means it might 
polish the varieties, so to say, imto species. 
(6) Supposing, on the other hand, the species to migrate into a new environment, 
either geographical or habitative, the possibilities which we have just discussed again present 
themselves with the addition of a new factor to determine which of them is to come into 
play. For clearly either one or more than one of the varieties might migrate, and it is 
probable that the effect of changed conditions on a single variety would be different from 
that which they would have on a group of varieties. In the one case we should have 
the new factor of isolation, in the other this would still be wanting. 
But here we are brought face to face with a difficulty due to our lack of 
knowledge of the reproductive physiology of the Decapoda. The above paragraphs dealing 
with the effect of a changed environment all presuppose that the varieties breed more or 
less true, that is, that at least the great majority of the offspring of members of one 
variety belong to that variety. If, on the other hand, any variety give rise plentifully to 
all, it is clear that the task of natural selection will be much harder, for it will have to 
reduce this tendency in the surviving varieties as well as to extinguish the unfitted ones. 
On this point, however, it is useless to say more in the present state of our knowledge. 
[Note. Jan. 16, 1902. Since the foregoing was written, Mr Bateson’s paper on “ Heredity, 
Differentiation, and other Conceptions of Biology” (Proc. Roy. Soc. Lx.) has appeared. It 
seems that I have reached conclusions somewhat similar to those outlined in the later pages 
of that paper. What I have called “varietal characters” are probably the same as those 
which are there called “specific variations,’ while the “normal variations” are with me 
“variations within a homogeneous species or variety.” If Mr Bateson’s conceptions, and the 
terms by which he designates them, be accepted, a very great advance in Systematic Zoology 
will be possible. But some confusion is likely to result if either of the terms “varietal” 
and “specific” be applied to phenomena which are at the base of both varietal and specific 
entity. Would not the word “specifactive” meet the case better ?] 
