410 THE FRESH- WATER LOCHS OF SCOTLAND 
The interpretation of the phenomena has, however, been the 
object of rather extensive studies, pubhshed in 1908. I take the 
hberty of merely mentioning the principal points in the investigations, 
and for the rest refer the reader to my main work. 
The seasonal variations do not occur, as hitherto believed, 
gradually through even transitional stages ; wherever the researches 
have been made at the right time or where samples have been taken 
at sufficiently short intervals, it has been proved that the seasonal 
variations are mainly completed in the course of a very short time, 
about tzvo to three weeks. It has been noticed, for example, that there 
Fig. 55. — Ceratium Mrundinella, Asplanchna jJTioclonta, Daphnia hyalina, Ryalo- 
daphnia cucullata, Bosniina coregoni (Fureso and Julso). Upper row : summer 
forms with increased floating power, June. Lower row : the same species as winter 
forms with less floating power, May. 
are species, e.g., Asplanchna priodonta, which in the course of about 
three weeks increase their longitudinal axis about five times ; that the 
distance from the eye to the point of the crest in Hyalodaphnia increases 
from about 100 to 600 m in the course of three to four weeks (Julso) ; 
and that the flagellum in Bosmina coregoni grows from 360 jj. to 800 ^ 
(Julso) in the same time. This means that whilst the joint stock of 
individuals in the species first had the measurements 100 /x {Hyalo- 
daphnia) and 360 /x (Bosmina coregoni) (lower row, fig. 55), the great 
majority of the individuals have got the new sizes about three weeks 
later (upper row, fig. 55). 
The time when the variations are completed is the same for all 
