40 
Proceedings of the Royal Physical Society. 
the thread-cells of the Tubularia, and found four kinds, two (large and 
small) of a nearly globular shape, each containing a four-barbed dart, 
and two (large and small) of an almond shape, the larger one containing 
a thread, furnished with a lengthened brush of recurved barbs. They 
then examined the papillae of the Eolis, and found the ovate sacs filled 
with an indiscriminate mixture of all the four kinds of thread-cells found 
on Tubularia indivisa. 4:th, Dr M'Bain and Dr Wright found a speci- 
men of JEolis Landshurgii on Eudendrium rameum. Eiulendrium 
rameum was furnished, as to the bodies of its polyps, with very large 
bean-shaped thread-cells, in which an unbarbed style could be detected, 
while the tentacles of the polyps are covered with exceedingly minute 
cells. They compared the thread-cells of the Eudendrium with those 
found in the sac of Eolis, and found both kinds identical. Lastly, Dr 
Wright had kept the specimen of Eolis Drummondii above-mentioned 
fasting for a long time, and then introduced it to a large specimen of 
Coryne decipiens fresh from the sea. The next morning every polyp 
of the zoophyte had vanished, and the ovate sacs of the Eolis were 
packed with the distinctive thread-cells of the Coryne, mixed with a few 
thread-cells of T. indivisa^ the remains of its former feast. He also 
found the thread-cells of C. decipiens in the alimentary canal. It was at 
one time supposed that thread-cells, or Cnidae, as Mr Gosse had named 
them, were only to be found in the hydroid and helianthoid polyps and 
the Medusae ; Professor AUman afterwards discovered them in a species 
of Loxodes, a protozoan animalcule ; and Dr Wright had the good fortune 
to find them on the tentacles of an annelid, Spio seticornis, and also on 
the tentacles of Cydippe, one of the Ctenophora. Since then he had 
observed them on the very minute tentacles of Alcinoe, another of the 
Ctenophora. In all these classes of animals thread-cells were developed 
within the ectoderm or skin of the animal, and in many, such as in 
T. indivisa, each within a distinct and very apparent sac, and not in 
connection with the digestive system. The type of structure, moreover, 
of the thread-cell in the Protozoon, the Polype-medusa, the Annelid, and 
the Ctenophore, was essentially different for each class ; and this fact 
alone would lead one to doubt as to the origin of the thread-cells of Eolis, 
which so exactly resembled those of the polype-medusae in their structure. 
Nevertheless, it was certainly a very strange fact, for a fact the author 
firmly believed it to be, that one animal should be furnished with appa- 
ratus for storing up and voluntarily ejecting organic bodies derived from 
the tissues of another animal devoured by it, and that these should still 
retain their destructive functions unimpaired ; and he stated that his 
friend Mr Alder, one of the highest authorities on the Nudibranchs, 
still hesitated to assent to the doctrine sought to be proved by the pre- 
sent communication, on the ground of its extreme improbability. 
