No. 2. — The Reactions of Metridium to Food and other Substances! 
By G. H. PARKER. 
Introduction. — The observations upon which the following account 
is based were made at the Newport Marine Laboratory in August, 1895, 
and it is with great pleasure that 1 acknowledge my indebtedness to 
Mr. Alexander Agassiz through whose kindness and generosity I enjoyed 
the privilege of working there. i 
The growing interest in the comparative physiology of the nervous 
system has shown itself in no way more forcibly than in the number and 
importance of the contributions to this subject in the last decade. These 
contributions, however, demonstrate the richness of this new field of 
research rather than its exhaustion, and point to a remodelling of the 
older physiologieal conceptions ou the grounds of wider observations. 
It is my purpose in dealing with the relations of actinians to their food 
to aid in some degree this general advancement. 
The stimulation of actinians by their food and other substances has 
been a matter of study only recently. In 1882 Pollock (82, p. 474) 
stated that, when pieces of mussel, limpet, etc., were placed near an 
actinian in a sea pool or salt-water tank, the animal responded by ex- 
panding its oral disk and moving its tentacles. This response was in- 
terpreted by Romanes, in an addendum to Pollock’s paper, as evidence 
of a sense of smell in these animals, a conclusion from which Jourdan 
(91, p. 131) dissented, in that he preferred to regard the response as 
a result of the stimulation of the organs of taste. 
In none of these earlier investigations was any attempt made to lo- 
calizo tho sense organs affected by the food, and it was not till 1891 that 
Loeb described, in connection with other matters, some experiments 
bearing upon this question. Loeb ('91, p. 67) studied several genera of 
actinians, — Adamsia, Actinia, Anemonia, etc., — and demonstrated that, 
amongst other organs, the tentacles were stimulated by the presence 
of food. The tentacles, however, were not the only parts capable of 
1 Contributions from the Zodlogical Laboratory of the Museum of Comparative 
Zoölogy at Harvard College, E. L. Mark, Director, No. LV. 
VOL, XXIX. — NO. 2. 1 
