16 
Proceedings of the Royal Society of Edinburgh. [Sess. 
change was noticeable. The exuviated cuticles of the former were 
translucent and almost devoid of green pigment, while those of the 
latter were identical with the cuticles of inter-moult animals. Above 
this size, there are no means of identifying immature pre-moult animals, 
hence it seems probable that maturity is reached before ecdysis. This, 
at any rate, is true of the females, which do not mate except in the 
post-moult condition. In the experiments here recorded, the pre-moult 
individuals employed were all sexually ripe examples. 
The largest series of individual immersions was carried out with inter- 
moult crabs, the results being shown in the two appended tables. The 
following conclusions may be derived from these figures : — 
(a) Sex has little influence on the result. This confirms Tait’s findings 
(13) in the case of Ligia. 
(b) Size has a marked influence, large crabs surviving longer thamsmall. 
While this finding is also similar to Plateau’s (10) and Tait’s (13), the present 
results, obtained with a series of animals of greater range of size, enable 
one better to appreciate the enormous influence of this particular factor. 
As an illustration, one may perhaps compare the shortest survival period, 
one hour ten minutes in a crab less than 1 cm. in breadth, with the longest, 
twenty hours in a crab of 7-8 cms. breadth. The tables also show the 
extreme limits of variation for each particular size. Variation may be due 
in part to the animals being at the extremes of their size group, e.g. the 
group IT-2'0 cms. Of the sixteen animals used, eleven were below 1*4 cm., 
with an average survival period of 3 hrs, 30 mins. ; one 1*5 cm., with a sur- 
vival period of 7 hrs. 30 mins. ; while the other four were above 1*7 cm., and 
had an average survival period of 8 hrs. 5 mins. Similarly, variation may 
depend on whether the animals are commencing or ending their moult 
phase. It has already been noted that mature pre-moult crabs below 5 cms. 
(males) and 3 cms. (females) were unprocurable ; hence below these sizes it 
is possible that immature pre-moult forms were immersed along with inter- 
moult animals (from which they are not readily distinguishable on account 
of their similarity in colour), giving rise to low survival periods. 
(c) Moult-cige has also a decided influence, survival being shortest with 
the post-moult crab, longer with the pre-moult, and longest with the inter- 
moult. This result corroborates Plateau’s (10) but would seem to negative 
Tait’s observations (14), though, in comparing the moult ages of Ligia and 
Carcinus, one has to bear in mind that the former moults in two stages. 
Thus the post-moult phase of Carcinus does not correspond to that of Ligia, 
but rather to the phase, “ between posterior and anterior moult,” in which 
the posterior half of Ligia is in a post-moult condition, while its anterior 
