20 E. W. SEXTON AND M. B. WING. 
blocking the oviduct, until another moult takes place and the plug is 
sloughed with the old cuticle. 
Another point must be mentioned in regard to the suitability of this 
species for laboratory work, and that is the ease with which it adapts 
itself to artificial conditions. This is probably due to the fact that it 
comes from brackish water ditches where it is habituated to great varia- 
tions of temperature, salinity, pressure due to depth of water, etc. The 
density, for example, varies to an extraordinary degree according to 
the season, tides, excessive rainfall or drought, ranging from 1 
to 1-028. 
In the experimental work, it has been necessary to keep the water as 
nearly as possible at the same salinity, as any sudden change of con- 
ditions always affects the animals’ growth and breeding. A mixture of 
one part of sea-water to six parts of fresh water gives the same density 
(1-004) as that found in the ditches when the animals were taken, and 
such water we have generally used. 
The best results have been obtained by keeping the animals in finger- 
bowls, generally one pair in a bowl. Each bowl contained about 200 c.cs. 
of water, and was covered with a glass plate to check evaporation and 
exclude dust. No aerating apparatus was used, the animals obtaining 
sufficient air for their needs from the surface of the water exposed in the 
bowls. In the same amount of water but with a smaller surface exposed 
to the air they did not flourish at all, as was found later when using jam 
jars and honey jars for the broods ; only a very small proportion of the 
young reached maturity. 
For food dry leaves of all kinds were used, after they had been allowed 
to rot in water. It was found that the animals preferred the soft tissues 
of the leaves of elm, hazel, and sycamore, rather than the harder leaves 
of oak, beech, ete. A fine delicate Ulva from the ditches they ate freely, 
but when the supply failed and the harder marie variety (Ulva latissima) 
was given, they did not eat it until it macerated. They flourish better 
and are much healthier with some of the mud from the ditches in the 
bowls, but in all these experiments we were obliged to keep the water 
clear, in order to watch the animals without disturbing them unnecessarily. 
The young are so minute—about 1 mm. in length when hatched—that 
they completely escape observation in the mud, clinging as they do to 
any particles of dirt or weed. 
The bowls were kept in ordinary diffused light, strong sunlight being 
avoided. 
