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NOTES:—ORIGINAL AND SELECTED.
FLATWORMS (TURBELLARIA).
Dalyellia viridis (G. Shaw) (Vortex helluo, Mull.).—
This interesting Turbellarian Worm was found in considerable
numbers amongst vegetation in a pond at Chigwell Row on
Saturday, 20th April 1912. The writer took specimens from a
pond in Richmond Park the week previously and has been
told that it has been seen recently in similar places in the neigh-
bourhood of Chingford. Dalyellia viridis is about 3/8inch
long and is, as its name suggests, green in colour. The colour
is due to an associated, unicellular alga. The worm is provided
with two small eyes. The alimentary system consists of a mouth
at the anterior end, a muscular pharynx and a blind alimentary
sac which serves as a stomach. The animal is hermaphrodite.
The chief point of interest is the animal's association with a
living unicellular alga, great numbers of which are present in
the body immediately beneath the colourless cuticle.
Professor Sekera, of Tabor, Bohemia, kept specimens under
observation for some time, and the following notes are taken
from the account of his observations. Young specimens were
taken in ponds in March when ice was still floating on the water.
The animals were colourless, but as soon as they approached
maturity and the sexual pore developed, it was noticed that a
few algal cells or "zoochlorellae" had entered the body cavity
by this means. Streaks of green granules then began to spread
from this region and extend beneath the cuticle over the whole
body until finally the animal became quite green. Solid food
in the form of diatoms, rotifers, etc., was ingested during this
period. While rapid division of the algal cells was taking
place, they formed spherical or ellipsoid clusters, each group
being surrounded by a colourless membrane. The mem-
brane finally disintegrated and the green algal cells dispersed
in streaky formation. The mature algal cells showed no signs
of an enveloping membrane. The animals, at this period,
showed a distinct tendency to crawl towards the light, but sank
to the bottom of the vessel at night. During the third week,
eggs were formed in the body cavity. Sekera says that he
never found more than 20 in one individual, but a healthy looking
specimen from Chigwell Row contained 49 ! The worms at
this stage began to avoid the light and spent the whole day at
the bottom of the vessel or under vegetation. During the first