412 THE FRESH-WATER LOCHS OF SCOTLAND 
weeks (figs. 56 and 57). During growth (fig. 58), and before the mature 
stage is reached, the body form is further remodelled : the result is a 
long and slender form, more suited to the new demands. After 
maturity the body is usually fixed in form ; it grows further, but 
retains practically the same proportions as in the last stage before 
A B C 
Fig. 56. — Two round-headed spring females (A and B) with pointed-headed young in the 
brood-pouch ; C, a pointed-headed autumn female with round-headed young in 
brood-pouch. 
maturity. This spring generation, which becomes the true bearer of 
the seasonal variation, is thus on the inception of maturity furnished 
with a different and greater floating power than the foregoing. The 
latter has been designated the last generation in the series of winter 
'^7 % Va ^Vio % '/z % '/6 % % % 
2J 22 16 16 11 4 12 1 9 12 14 14 IS 
Fig. 57. — Hyalodaphnia cucullata. Seasonal variation in the newly hatched young 
(Fureso). The young are hatched with high crest in summer, but round-headed 
and without crest in winter. Highly magnified. 
generations ; the former, the first in the series of summer generations. 
The direction now taken by the variations increases in all successive 
generations until the water has attained its highest temperature ; but 
the difference between two successive generations is now never so 
great as between the two above mentioned, when the temperature 
of the water is lower (14-16° C). Sometimes the demands made by 
the outer conditions on the floating power of the species are so great 
