264 
Proceedings of Royal Society of Edinburgh. [sess. 
The Pallial Complex of Dolabella. By J. D. P. G-ilchrist, 
M.A., B.Sc., Ph.D. Communicated by Professor Ewart, 
F.R.S. {From the Natural History Laboratory of the Uni- 
versity of Edinburgh.) (With a Plate.) 
(Read May 28, 1894.) 
The following account the pallial complex of the Tectibranch 
Dolabella is, as regards the minuter details, founded on a single 
specimen {Dolabella rumphii) kindly sent me by Professor MTntosh 
of St Andrews. By an examination of the collection in the South 
Kensington Natural History Museum I was enabled to verify for 
the genus points which might have been peculiar to this species, 
and in one point to note an important variation. 
A few words as to the necessity of an accurate description of the 
pallial complex or system of organs in the mantle cavity of the 
Opisthobranchiata^ and the inferences that may be drawn, may not 
be out of place. 
Just as a large group of the Mollusca, the Prosobranchiata^ is 
characterised by the possession of a shell, and the whole organism 
is moulded and conditioned by this shell, so another group, the 
0]pisthobrancJiiata^ is characterised by the getting rid of this shell, — 
a process which draws in its train the most thorough-going changes 
in the different organs, especially those of locomotion. The foot 
becomes largely developed, the shell disappears or becomes en- 
veloped by the mantle, the viscera descend into the foot, and, most 
important of all, as throwing light upon the problem of the twisting 
of the Molluscan body, the various organs tend to return to their 
original position at the hinder end of the body. Deprived of its 
cumbrous shell there are opened up to the animal modes of life 
previously unattainable. It may become semi- or wholly pelagic, 
may crawl about freely among tangled sea-weed, or find its way 
readily through sand and mud ; and these new conditions of life in 
their turn give rise to new modification of organs. It is this that 
makes the parapodial and pallial organs of the Opisthobranchiata 
