60 Proceedings of the Eoyal Society of Edinburgh. [Sess. 
aspect and of the limbs of the animal are normally devoid of chromato- 
phores ; these in their shining clearness now stand out conspicuously 
against the dark chromatophore-bearing patches. A few parts are tinted 
light yellow, viz. the dactylopodites, the tips of the uropods, and the 
antennary flagella; otherwise the general hue is a clean grey. 
As time goes on the cuticle becomes less transparent and dark in 
colour. The hidden parts of the gills gradually get coated with a dirty 
fur of black material. The extremities of the limbs, of the antennae and 
of the uropods, change from yellow to red. By the depth of this redness 
one can best estimate the relative age of the cuticle. 
These facts are here set down because, as we have seen in the first 
communication of the series, it is important in the case of immersion 
experiments to know whether a given animal has recently moulted or not. 
Moreover, blanching of the animal when placed on a white background — 
see Tait (1910) — is much more manifest when the cuticle is new. 
Some days before moulting a chalky whiteness begins to develop on 
the ventral aspect of the anterior four (free) thoracic segments. At first 
limited to the narrow sternites, the whiteness invades the non-calcified 
parts, and eventually the whole anterior ventral aspect looks chalky. 
This whiteness, found also in similar circumstances in the other 
Oniscoidea but apparently not in any marine or fresh-water isopod, is 
by Herold attributed to the development of definite plates, rich in 
calcium carbonate, just underneath the old cuticle. Herold’s statement 
I am in a j)osition neither to dispute nor to confirm. The idea that the 
chalky appearance might be due to inclusions of air was rendered im- 
probable by the fact that it develops in Ligise completely immersed in 
sea-water. When the overlying cuticle is shed no sign of whiteness 
remains on the animal, nor does the exuviated skin appear white. One 
observation bearing on the subject is worth recording. A Ligia immersed 
for thirty-four days in half sea-water died in the act of moulting 
the posterior half of its cuticle. In this animal the usual chalky 
appearance had failed to develop, whereas all Ligirn that underwent 
moult during immersion in full-strength sea-water exhibited the local 
white coloration. 
As the ventral whiteness increases in area the dorsal aspect of the 
four anterior segments likewise alters in appearance. One obtains an 
impression as if the cuticle in this region were slightly separated from 
the underlying parts ; the colour is lighter, and the deeper parts can no 
longer be clearly seen through the old cuticle. This part of the body 
seems also harder than usual to the touch. At the present stage the 
