POND LIFE AT BRAMHALL. 253 

minute pond-life such as the Polyzoa, Infusoria, and Rotifera, for 
with the aid of the microscope we are enabled, from the transparent 
nature of their organs, to trace their development from the very 
commencement of their existence; and thereby solve some of the 
important Biological problems pertaining to the life of the highest 
organisms. 
Cyclops quadricornis and Daphnia pulex, two entomostraca found 
in every pond nearly all the year round, well illustrate the immense 
fecundity of these minute animals, for we are told that according to 
a computation by Irvine from data ascertained by actual observa- 
tion, a single fertilized female of the common Cyclops may be the 
progenitor in one year of over “four thousand million” young. 
The genus Cyclops receives its name from possessing only a 
single eye or cluster of ocelli; the Daphniz and most other ento- 
mostraca having the same character. Their motion through the 
water consists of a series of jerks caused by striking the water with 
their tails, feet, and antennz. 
The feet and tail of the Cyclops are adorned with plumose tufts, 
and it is a very voracious creature, feeding on other minute 
animals and even on its own young; while the Daphnia derives 
its sustenance from particles of vegetable substances. 
Among aquatic insects were Notonecta and the larvee of the 
Agrionid ; a family of Dragon-flies, as well as Dytiscus in both 
the larval and mature forms. The more important finds were, how- 
ever, the following. The Phantom Larva, Corethra plumicornis, 
was caught by the hundred, and its pupa by the dozen. This larva 
of a dipterous insect is peculiarly interesting to microscopists on 
account of its wonderful transparency, which enables its anatomy 
to be studied without dissection. Its most remarkable internal 
feature is the kidney-shaped air-sacs, two of which are situated in 
the second and two in the ninth segment of the body. They are 
spotted with oval cells of black pigment, which gives them a most 
beautiful appearance when properly illuminated. The larva is 
destitute of the longitudinal trachea found on other larvee, but in 
the pupal state the air sacs disappear, and tracheal trunks are de- 
veloped. 
The nymphs of two genera of the Ephemeridz were also found, 
Cléeon and Heptagenia. The former is recognized by the external 
gills of the first six abdominal segments being composed of double 
plates ; the seventh pair being single. The latter is known by the 
gills on the first six segments being formed of single plates, to the 
roots of which are attached bundles of threads, the analogues of 
perfect gills. The two nymphs differ also in their mode of loco- 
motion. Cléeon swims by sudden jerks of the abdomen, whereas 
Heptagenia is generally found creeping or running along the ground. 
They both lose the central filament of the tail on assuming the 

