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THE ESSEX NATURALIST
NEPIDAE
Nepa cinerea L. Gt. Baddow, Galleywood, Springfield, Danbury.
VELIIDAE
Velia caprai Tamanini: adults and nymphs from running water at
Springfield. Formerly only one species of Velia was recognised as British;
V, currens. F. It has recently been shown that the British Velia consist
of two species, neither being V. currens, but V. caprai. Tamanini and V.
saulii. Taminini. V. currens, is recorded for Essex and these records
can probably be referred to V. caprai, which would appear to be the
commoner species.
GERRIDAE
The pond-skaters have been little collected, but Gerris lacustris L. is
the species usually met with. G. thoracicus Schum. has also been found
at Galleywood.
Free-Living Nematodes from
Skippers Island
BY JOHN W. COLES
Department of Zoology, British Museum (Natural History)
This note is intended to be a contribution to the general ecology
of Skippers Island in the parish of Thorpe le Soken, Essex; and
is based on nematodes extracted from six samples of soil and mud
collected by Mr. E. F. Williams and Mr. A. C. Wheeler.
The Nematodes are of universal occurrence—free-living in the soil,
among water weeds and in the bottom deposits of both fresh and salt
waters; parasitic in vertebrates, insects and other invertebrates; and
parasitic on the roots, stems and leaves of plants (where they are com-
monly known as eelworms). Although the numbers of parasitic nema-
todes are very great in both individuals and species, the free-living
forms are even more numerous. The vast majority of these, however,
are minute, varying from microscopic to a few millimetres in length.
If the material in which they are living is examined under a lens
they are seen as transparent thread-like worms, tapering more or less
at the extremities. They can be readily distinguished from other minute
worms by their type of movement, which is always eel-like and without
change of size or shape of body. Although they are unsegmented,
when examined under high magnification the outer covering or cuticle
exhibits transverse striations, much more marked in some forms than
others. Many, in fact, appear to be quite smooth.