42 
ON THE STRUCTUEAL CHANGES 
ACCOMPANYING THE ECDYSIS OF THE CRAB 
CANCER PAGURUS. 
By E. P. WITTEN, B.Sc. 
(From the Royal College of Physicians’ Laboratory, Edinburgh). 
The following paper embodies the results of my observations on j 
the histological structures in the soft and the hard crab. Since t 
the preliminary paper of a year ago, I have pursued the subject | 
at the Marine Laboratory, Cullercoats, and continued it at the i 
Laboratory of the Royal College of Physicians, Edinburgh, and for j 
the facilities afforded me at both places, I now beg to tender my j 
sincere thanks. 
The macroscopic changes which occur at the period of ecdysis ^ 
are well known, and it will be useful to briefly recall some of the : 
facts so far as they relate to the problems considered in the present i 
investigation. In the first place there is the phenomenon of i 
sudden expansion so strikingly impressed on seeing the soft crab ' 
emerge from the shell and settle down heside it having increased 
say about one-fourth of its original size. To explain the phenomenon 
is certainly difficult. The simplest explanation is to assume as is 
usually done that the tissues have been growing over the whole 
period since the last ecdysis. This, however, does not appear to be 
the case. Microscopic examination does not favour this view, nor 
does an experiment which Mr. Meek has several times made. He 
carefully stripped off the hard shell from shore crabs about to cast, 
in most cases very completely, and succeeded in keeping them alive 
for several hours afterwards. The crabs remained, however, of 
precisely the original size. This experiment points to the conclu- 
sion that the expansion is not due to a gradually increasing 
pressure from the growth of the tissues, but rather to a sudden 
