1917-18.] Period of Survival of Shore-Crab in Distilled Water. 15 
that wide-mouthed bottles, provided with caps or lids to prevent escape, 
were used to hold the animals. A separate bottle was at first used for each 
crab ; at a later stage selected groups of animals were immersed together 
in a large container provided with two or three aeration tubes. 
Before immersion in its bottle, each crab was weighed ; the breadth 
of the carapace between the two most widely separated points was also 
measured. Thereupon each animal was washed in a vessel, first under 
running tap- water, and then in three changes of distilled water. The 
washing process lasted about ten minutes ; the time of immersion was 
reckoned from the first contact with tap-water. Tests carried out with 
silver nitrate solution showed that the preliminary washing suffices to 
remove all but the merest trace of externally adhering salts About 
0 01 per cent, of chlorides remained. The crab was finally immersed in 
20 times its weight of distilled water, and there left till all respiratory 
movement had ceased, whereupon the animal was again weighed, after 
being shaken free of water and wiped with a cloth. Groups of crabs 
immersed in one dish were treated in essentially the same way. Over 
one hundred individual immersions, apart from group immersions, were 
made. 
Experimental Results. 
It being necessary to classify the crabs according to the phase of 
moult, a threefold grouping was adopted, viz. (1) those just moulted, 
(2) those intermediate between two moults, and (3) those approaching new 
moult. These phases may, for shortness, be designated post-moult, inter- 
moult , and pre-moult respectively. Crabs in the post-moult phase are 
of course unmistakably distinguishable by the softness of the cuticle ; 
they are brownish dorsally and yellowish ventrally. In the inter-moult 
phase the shell is conspicuously clean, the articular membranes are 
colourless, while the animal as a whole is green dorsally and white to 
green ventrally. Animals in the pre-moult phase have red articular 
membranes; they are dark green dorsally and orange to red ventrally, 
and sometimes — more especially the males — exhibit dirty-looking ex- 
cavations and perforations of the carapace. According to Smith (11), 
those animals with red articular membranes are sexually mature. The 
most careful search failed to discover red pre-moult crabs below 5 cm. 
(males) and 3 cm. (females), indicating that maturity is only attained at 
these sizes. Five animals below 5 cm. were observed during the process 
of moulting. In two, the short pre-moult phase was characterised by 
the passing of the green colour of the inter-moult condition to one of 
greenish grey and finally to a dirty grey; in the remainder, no colour 
