152 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
In a small pool near Wurzburg, dry every summer, 
he finds Daphnids and Asplanchna. In another close by, 
._ Cypris, Culicidee, and fly-larvee, and these are never assoc- 
lated with Daphnids. When the conditions are favourable, 
development proceeds at a rapid rate. Thus in 1883 
the summer was very dry in south Germany; no rain had 
fallen for weeks. One night a heavy thunderstorm broke 
and two days afterwards, v. Kennel found in rain-pools not 
only Infusoria, Ostracods, Mesostomid Turbellaria with 
winter-eggs, but also Branchipus with ripe eggs. The next 
day all was dry as before. How far passive migration 
has occurred in the case of P. alpina it is difficult to 
ascertain. At Wurzburg, neither fish nor birds visit the 
spring where it is found. But this does not hold for 
other localities where I haveseen it. If we keep in mind 
that it is at the point where springs reach the surface that 
this form chiefly occurs, it is not difficult to accept v. 
Kennel’s supposition (before the eggs were known) that 
the real habitat of this animal is in the interior of moun- 
fains and in subterranean water and we are driven to the 
conclusion that the animal must have ranged over western 
Europe before the glacial epoch, acquiring its present 
distribution owing to the separation of England, Ireland 
and Isle of Man from the Continent and one another. 
Now however that the egg-capsules have been discovered, 
if appears more probable that a passive agency has been 
the main factor in a post-glacial process. 
2. Polycelis cornuta, O. Schmidt (Pl. XII, fig. 5.) 
This species occurs commonly in fresh-water in the 
neighbourhood of Port Erin, but in warmer water than 
Planaria alpina. 
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