102 
THE ESSEX NATURALIST. 
it is stated that on September 26, 1905, Mr. R. Vallentin col¬ 
lected Chirocephalus in a roadside pond, between Gwinear Road 
Station and Helston, but that a week later not a single speci¬ 
men was to be found. Dr. A. S. Packard, the well-known 
American authority on the Phyllopods, has also placed on record 
a similar case of the rapid disappearance of these creatures. 
Now, such experiences, although very disappointing from 
one point of view, are also exceedingly interesting, and they 
at once start us asking questions as to the reason for the 
phenomena. Mr. Vallentin, in the case referred to, imagined 
that the disappearance might be due to a herd of cattle on their 
way to Helston market having rushed into the pond and killed 
all the specimens ! Dr. Packard thought that it was a question 
of temperature and that with the approach of warm weather 
all the animals died off. 
My own opinion is that the sudden disappearance is due 
to enemies in the pond itself—Ostracods, Insect larvae, etc. 
-—and this leads to the conclusion that Chirocephalus probably 
cannot maintain itself in an ordinary pond, where it has to com¬ 
pete with the commoner forms of pond-life. This would explain 
why it is usually recorded from small, non-permanent pools, 
cart-ruts, etc., just the sort of places, in fact, where competition 
is presumably at a minimum. It would also explain why 
Chirocephalus appears to be so comparatively rare. It may 
be supposed that it does actually commence to develop (from 
eggs carried about by birds and in other ways) in many more 
ponds than we imagine, but that it is soon disposed of by some 
of the other inhabitants and in consequence collectors do not 
chance to find it. 
The sudden appearance of Chirocephalus in places where it 
has never before been seen is just as remarkable a fact as the 
sudden disappearance above alluded to. It is no doubt due to 
the eggs retaining their vitality for long periods, even after be¬ 
ing frozen or embedded in dried mud, and to their distribution 
over w ide areas by birds and other agencies. 
There are a good many records now, mostly in the last fifteen 
years, of the occurrence of Chirocephalus in England, but 
they are mainly from the more southerly counties. The 
most northerly record that I know of is from near York (speci¬ 
mens in the British Museum). There are no records so far 
from 'Wales or Scotland or Ireland. 
