51 
1916-17.] Experiments and Observations on Crustacea, 
“ without appearing to be in any way affected by the immersion.” In 
“ fresh ” (presumably tap-) water Ligirn did not survive more than two 
days. The internal gill-lamellae of these last specimens were much swollen 
owing to absorption of water, the external lamellae being little affected. 
It was claimed that immersion in sea-water produces microscopic changes 
in the internal gill -lamellae ; no change, however, could be detected on 
superficial examination. 
Details concerning Technique , etc. — In the present investigation four 
immersion fluids were used, viz. sea- water, half sea- water, quarter sea- 
water, and distilled water. Each animal, after being washed in successive 
changes of the appropriate fluid, was immersed by itself in 150 c.c. of 
fluid in an Erlenmeyer flask, the water being aerated from a glass capillary 
that dipped below the surface out of reach of the gills (this last condition 
is specified because, when the aeration-tube dips deeply, bubbles of air 
may attach themselves to the gills). By having a large battery of flasks 
attached to the same aeration-pump — one of Dr J. F. Gemmill’s many 
ingenious devices for this purpose — it was possible to conduct a great 
number of immersion experiments simultaneously. The water in the 
flasks was changed at suitable intervals. The temperature varied between 
10’5 and 14\5 degrees Centigrade, the experiments being carried out from 
mid- January to mid- April. Permanent cessation of gill-movements was 
taken as the sign of death. 
A word as to the manner in which the supply-stock of Ligia was kept 
in the laboratory. Previous experience (5) had shown that Ligia long 
survives if kept without food simply in a damp atmosphere. On this 
occasion an attempt was made to find a suitable food. When not provided 
with food they eat each other ; they also eat Orchestia, if these are 
supplied. They refused to eat Porcellio ; likewise pieces of cooked bacon 
or chicken. When blades of Laminaria digitata were provided they re- 
frained from murder of their own kind and of Orchestia, and ate the 
vegetable matter freely. They showed distinct preference for Laminaria 
as compared with Fucus nodosus and Fucus vesictdosus. The animals 
lived in hundreds in a large tin box, which was kept closely covered. To 
maintain the atmosphere moist a piece of linen wrung out of half sea- 
water was laid inside. Twice a week the whole batch of animals was 
removed and bathed in three successive changes of clean sea- water ; at 
the same time their box and the piece of linen stuff were thoroughly 
cleansed under the tap. Kept in this way the animals throve exceedingly. 
Practically the only deaths were those of moulting individuals, which are 
apt to get trampled upon. 
