406 THE FRESH-WATEK LOCHS OF SCOTLAND 
spherical form and make it cylindrical or torpedo-like, since the 
cylindrical form, supposing that the body is held horizontally during 
sinking, is able to afford a greater cross-section resistance than the 
spherical. Some flagellates {Ceratium hirundinella) project horizon- 
^"7? % % %. % % % 2% % % % % 
21 22 16 16 '11 ^ 1 2 1 it 5 9 12 1^ 'Ih 15 
Fig. 52. — Seasonal variation in Hyalodaphnia cucullata (Fureso) and Daphnia hyalina 
(Esromsb). The two may best be regarded as two races (modifications, phenotypes) 
of the same species. In summer the crest is much higher than in winter, and the 
whole form more slender. The upper row of figures gives the date, the lower the 
temperature of the water in degrees C, 
tally from the side of their body a long spine which, as it is inserted 
at right angles to the direction of sinking, augments the cross-section 
resistance. Very many organisms belonging to all the animal 
1/ 15/ 15/ 20/ 15/ ::!/ 5/ 2/ 30/ 31/ 
/8 h 110 lU ll U 15 /e 16 17 
22 12 12 6 1 3 6 13 16 15 
Fig. 53. — Bosmhm coregoni, seasonal variation (Julso). In the summer half-year the 
animal is higher than long ; in the winter half-year, longer than high ; the antennae 
are more than twice as long in summer as in winter. The eye is largest in winter. 
This seasonal variation we do not understand. 
plankton groups try, through diminution of the volume, to augment 
the surface. In this case the surface is often covered with a coatins: 
of small asperities ; also by this means a diminution in the rate of 
sinking is probably attained. 
Even if the physical interpretations are not in all cases quite satis- 
