231 
[WORK FROM THE PORT ERIN BIOLOGICAL STATION. | 
NOTES on the HAMAL and WATER-VASCULAR 
SYSTEMS of the ASTHEROIDEA. 
By Herspert C. CHADWICK. 
With Plates XXXVI to XXXIX. 
[Read 10th March, 1893.] 
HIGHTEEN months ago, at the suggestion of Prof. Milnes 
Marshall of Owens College, I undertook a re-examination 
of the structures which together form what is commonly 
known as the blood-vascular system of the Asteroidea. 
To those who are acquainted with the literature of the 
Echinodermata, especially that published during the past 
twelve or fifteen years, such a research may, at first sight 
appear quite superfluous, the structures just named having 
been described by Ludwig, Perrier, Hamann, Cuénot, and 
quite recently by Durham. I was, however, fully aware 
that a certain amount of scepticism existed in the minds 
of other workers in the same field, as to the accuracy of 
the descriptions given by one or other of these zoologists, — 
and on that account was not unwilling to examine some 
of the doubtful points for myself. Though not yet quite 
complete, my work is sufficiently far advanced to warrant 
my acceptance of the invitation of the Council of the 
Liverpool Biological Society to submit my results for the 
consideration of its members. The close anatomical rela- 
tion in which the so-called blood-vascular system stands 
to the water-vascular system has led me to a study of the 
latter scarcely less detailed than that of the former, and 
for convenience sake I shall discuss the two systems 
together. 
