53 
ON THE 
ACCOMPANYING 
STRUCTURAL CHANGES 
THE ECDYSIS OF THE 
CRAB. 
By E. 1*. WITTEN, D.8c., Dckuam College of Science, 
N K WCASTI.K- UPON - T V N K . 
At the request of Mr. Meek, [ lmve commenced to investigate 
the changes which occur during the growth of the Crab and 
other Crustacean forms, with special reference to exuviation. The 
subject has attracted the attention of observers since the time of 
Aristotle. In this way there has gradually been accumulated a 
number of valuable facts relating especially to the external changes 
accompanying the process of eedysis. In this preliminary account, 
however, I do not intend to make detailed reference to this 
historical side of the question. But it is impossible to approach 
it without mentioning that Vitzou', in 1882, made a very careful 
analysis of the ectoderm and its chitinous products discussing 
separately the external shell and the proctodeal and stomatodeal 
invaginations of the alimentary canal. But since that time little 
has been done in the direction of ascertaining the effect which 
the preparation for, and the eedysis itself have upon the different 
tissues and organs. 
The following notes are based on the examination of 3 soft and 
8 hard crabs, 2 males and 1 female in each case. These were 
brought from Beadnell on November 27th, having been captured 
by Mr. Douglas, and some of the points which we have observed, 
if not showing anything new, are still interesting enough to excuse 
this preliminary account. 
We might say that there are four main causes which lead us 
to expect morphological changes in the tissues of most of the 
arthropod forms during the process of exuviation. Firstly, the 
old shell must be cast off and a new one produced. Again, it is 
only when soft that extension of many of the tissues and organs, 
which have probably been growing since the last eedysis, can 
take place. Thirdly, the various members have to be withdrawn 
from the many nooks and corners of the old shell, in some parts 
1.— Vit*ou. Kri'hrrrhee «ur la structure rt la lonuati .n do teguments .-he/ Its ■ ru-tao- 
ddcupodes. Archive* de Z >ol. Exp^r. et General. 
