43 
pressure produced more than probably during the process. And if 
this be ultimately proved to be the case, it is safe to say that the 
pressure is produced by the ingestion of water and its absorption 
probably through the digestive gland. 
The blood plasma undergoes an enormous increase in volume 
during ecdysis, and the condition is maintained in a gradually 
diminishing degree until the completion of the process of calcifica- 
tion. It is for this reason that the name “ watery crab ” has been 
applied to the “caster.” I have obtained as much as 250 c.c. 
of blood from a large soft crab. The increase I have presumed to 
be due to the ingestion and assimilation of sea water as stated 
above. With the increase in the volume there is associated an 
increase in the number of blood cells. Cuenot^ has pointed out that 
these arise from the lymphatic gland which is situated about the 
ophthalmic artery, and on the roof of the stomach ; and during the 
period of hardening, the cells of this gland are undergoing active 
proliferation. On the subsidence of the blood plasma to the degree 
demanded by the new stage in growth how far these cells persist is 
yet uncertain, for the relation between the condition of the crab 
and the number of blood corpuscles is not known. 
The excess of blood plasma is more than enough to occupy the 
increased volume of the blood sinuses, and it may therefore be 
presumed that it gives the internal pressure necessary for the 
jirocess of casting, and the gain in size, and also that it furnishes 
the turgidity connected with the subsequent proliferation and 
growth of the organs and tissues. This internal pressure was 
observed by llbaumur,'^ but received a different explanation. He 
found that the new shell was hard to the touch, and assumed that 
the condition was due to the muscles being in a state of cramp. 
Immediately after casting, the soft shell or cuticle consists only 
of the outer two layers, but the third or calcified layer begins to be 
laid down at once. This layer in the exposed region is by far the 
greatest in thickness, and as Mr. Meek has shown it takes mouths 
for the completion of the process, in the adult condition. The thin 
fourth layer is deposited after the completion of the third. 
The attachment of the shell to the underlying tissues is 
extremely feeble except at the parts where muscles originate or are 
inserted. In these regions the epithelial cells are very prominent, 
J ■ — Cudnot : Etudes physiolo^ques sur les Crustic^s D^capodes. 
Archives de Biologic T. xiii., 1895. 
2. — Reaumur: Observations sur la mue des Ecrevisses, etc., Xlem. de I’Acad. des 
Sciences, 1'18. 
