2 
1901] MICROSCOPICAL JOURNAL 323 
ed by the 12 mm. apochromat, 5-6ths axial cone, and a 
Huyghenian eyepiece magnifying about 45 times, the 27 
compensating ocular not proving sufficiently powerful 
for the purpose with this objective. 
Larval Water-mites on Aquatic Animals. 
C.D. SOAR, F.R. M.S. 
In a paper on Hydrachnidae, read in 1896, (Journ. Q. 
M. C., Vol. VI., p. 318), I mentioned that I wished to 
make myself familiar, as far as possible, with the larval 
forms of water-mites, and by a systematic search among 
all kinds of our pond-life to find out upon what creatures 
these larvae occurred, and if the same species was always 
parasitic on the same host. Since then I have collected 
and examined a great many aquatic insects, etc., but the 
results sofar have beenrather poor. They have, however, 
been considered sufficiently interesting to put on record. 
One of the most common aquatic insects upon which to 
find the larvae of Hydrachnidae is Coriza geoffroyi. I 
have found a great number of these, and some of them I 
have succeeded in keeping alive long enough to allow the 
red globular water-mite larvae to drop off and become 
free-swimming. ‘The latter always turned out to be the 
nymphs of one of the species of the genus Hydrachna, 
In September, 1898,0n the Norfolk Broads, I took a 
number of water-boatmen, Notonecta glauca, afflicted with 
the redglobular parasites. I brought some of them home, 
but, although I kept one or two alive for a long while, I 
did not succeed in getting any of the larvae to arrive at 
thenext stage. In the springof 1899, I again paid avisit 
to the same neighborhood, and succeeded in capturing 
some more water-boatmen. A number of these were 
brought home alive, as before, and this time I was success- 
ful in getting some of the red globules attached to the 
legs and body of the water-boatmen to become free-swim- 
