1916-17.] Experiments and Observations on Crustacea. 67 
going change, chiefly perhaps owing to the work of the lamented G. Smith * 
(1912, 1913) — cf. also Robson (1912). Smith established the existence of 
profound cyclic metabolic changes in the crab, which were not mere 
questions of calcium metabolism (Reaumur, strange to say, first proved 
the existence of the latter). His investigations included metabolism of 
glycogen, of fat and of blood pigments, in all of which cyclic change, 
related to the moulting periods, was detected. Arguing from the work of 
Potts (1906) and of Sexton and Matthews (1913), he declared that £ > growth 
and moulting are not necessarily connected processes,” and that “ moulting 
may take place without growth.” 
While the last conclusion was not absolutely warranted by the facts 
adduced in its support, it is certain that Smith’s general contention, so far 
as it implies disavowal of the Reaumur conception, is correct. The results 
obtained in such a simple way with Ligia prove that moult may be inde- 
pendent of immediate intake of food. Whether the result applies to all 
Crustacea is another question. Smith singles out for special mention the 
fact that ££ starved or underfed crabs never moult in an aquarium, however 
near they may be to the moult when captured.” 
In a recent paper Paul and Sharpe (1916) thus express themselves: 
“ Moulting is only the most noticeable part of a cyclic metabolic change in 
the crab. It comes at the end of a period when storage of reserve material 
has been the chief business of the animal.” The Ligia experiments are in 
full accord with the first of these two statements, the significance of which 
they even extend ; but hardly with the second. 
For a further point of physiological interest in connection with moult 
the reader is referred to the immediately preceding communication of 
this series. 
Summary. 
(1) Ligia, like other iposods, moults in two stages. First the covering 
of the abdomen with that of the posterior three thoracic segments is ex- 
uviated. About four days later the anterior covering is thrown off. The 
external changes that occur in the cuticle as it ages, and the behaviour 
of the animal during moult, are described. 
(2) At the moult the cuticle splits in two main directions : (i) transverse 
between the fourth and fifth (free) thoracic segments; (ii) longitudinal, 
at the coxotergal junctions of (free) thoracic segments 2 to 7, there being- 
no coxotergal split in segment 1. Coxotergal splitting is an arthrostracan, 
if not a peracaridan, feature. 
* Killed in action. 
