Thread-cells of the EoUdce. 
39 
of the Eolidse contains at its extremity a small ovate vesicle, communi- 
cating, through the biliary sac, with the digestive system, and opening 
externally by a minute aperture at the end of the papilloe. This vesicle 
is found crowded with compact masses of thread-cells ; which masses, in 
Eolis nana, consist of aggregations of small and large thread-cells, iden- 
tical in size and shape with those of Hydractinia, — on which this Eolis 
preys, — not contained in capsules, but cemented together by mucus. 
When we consider that each of the vesicles is in indirect communication 
with the stomach, I think we may, without presumption, suggest that the 
masses of thread-cells found in Eolis nana are quasi fsecal collections of 
the thread-cells of Hydractinia, which, protected by their strong coats, 
have escaped the digestive process. In corroboration of this view, I may 
mention that the thread- cells of Eolis papillosa, as figured in the work 
of Alder and Hancock, have a perfect resemblance to those found in the 
Actinias, which last animals furnish an Abyssinian repast to these car- 
nivorous mollusca." Dr Wright afterwards found that, as to the above 
idea, he had been anticipated by his friend Mr Gosse, who, in his 
" Tenby," after noticing the existence of the thread-cells in the papillae, 
remarks: — " The inquiry I suggest would be. How far the presence of 
thread-cells might be connected with the diet of the mollusc? And 
whether, seeing the forms of the missile threads vary in different genera 
of zoophytes, the forms of the corresponding organs in the papillse of the 
Eolides would vary if the latter were fed exclusively first on one and 
then on another genus of the former." He afterwards found that Mr 
Huxley had also doubted, previously to Mr Gosse and himself, whether 
the thread-cells of the Eolidse were not adventitious. Here were three 
independent observers to whom the idea has suggested itself ; Mr Huxley 
had first hinted it ; Mr Gosse suggested it, and how it might be found to 
be true ; Dr Strethill Wright also had suggested it, and given two in- 
stances in corroboration of his opinion, and to-night he proceeded to de- 
tail observations which would, he hoped, entitle it to be enrolled as a 
proved fact in the records of science. 1st, A specimen of Eolis nana 
was brought home from Morison's Haven, on a shell covered with Hydrac- 
tinia, taken from a rock-pool, in which was a profuse growth of Cam- 
panularia Johnstonii. The papillse of this Eolis contained the two 
kinds of thread-cells which are found on Hydractinia, together with the 
large thread-cells which occur within the reproductive capsules of 0. 
Johnstonii. 2d, An Eolis coronata was taken at Queensferry, on a 
massive specimen of Coryne decipiens, which was very abundant there. 
The thread-cells of 0. decipiens were very distinctive, being very large, 
oval, and containing a four-barbed dart. The thread-cells of the Eolis 
and Coryne were carefully compared together, and were found to be 
identical, od, Dr M'Bain and Dr Wright found an Eolis Drummondii 
on a fine specimen of Tuhularia indivisa. They first carefully examined 
