408 THE FRESH-WATER LOCHS OF SCOTLAND 
conclusions one is obliged to draw are of serious importance in 
systematic aspects. Everyone who has systematic knowledge of the 
animal and plant groups dealt with here knows that the specific 
characters are based especially just on the course of the contour-lines ; 
this applies to the plankton Diatoms, Desniidiaceae, Ceratium, Rotifers, 
and Cladocera. As we may now assume that wide limits, just with 
regard to the course of these contour-lines, can be considered as a 
conditio sine qua non for the occurrence of all these organisms in the 
pelagic region, we see that these contour-lines in the plankton 
organisms must be subject to the greatest possible variation. So 
long as there was not the least conception of this, the study of the 
plankton led to innumerable species being set up, which have now 
been reduced to some few : 30 Anursea species have become 4, about n 
100 Bosmina species and varieties 2, about 100 Daphnia species and 
varieties 1 or I have called the old species "races,"' and objection 
has been raised against this, perhaps with justice : they should most 
probably rather be called modifications (or " Phenotypes," Johannsen). 
It is very obvious that the naturalists who have dealt with these 
groups systematically and have created the many species should find 
it difficult to allow these species to be reduced to definite generations, 
broods, skin-changes (casts), produced by and adapted to definite 
outer conditions. Opposition towards the new views is quite natural. 
When, however, the naturalists of the older school treat the newer 
views of the species within the plankton community as loose theories 
which can be dealt with by loose, cursory criticism, whilst at the same 
time they demand that their views are to be considered as resting on 
an exact, scientific basis, they must be taken to task. Whatever 
systematic conception is taken as basis, one thing all should be agreed 
. upon : the notion of species within the lower organisms is always 
of a distinctly hypothetical nature. The setting up of the numerous 
species within the plankton organisms was not at all of a less 
theoretical nature than to reduce them to some few, as at present. 
In every view^ of species there is a certain element of the investigator's 
own individuality. With some the conception of species becomes more 
and more restricted with years : these are the naturalists who are 
so fortunate as to be honoured with the title " exact scientists." 
.With others the conception becomes ever wider and wider ; it is 
different at different times and hardly the same within the different 
countries.^ 
1 In a work just published ("On Synchceta fe7i?iica, sp.n.," Joum. Roy. Micr. Soc, 
1909, p. 170), Rousselet contests my view of the Synchseta species as seasonal 
forms. When Rousselet maintains that I have " expressed the opinion " that the 
Synchgeta species " are only seasonal variations of one species," this seems to me 
a bad starting-point for his criticism, and one which he is scarcely entitled to 
