STRETHILL WRIGHT, ON THE EOLIDE. 55 
Ctenophora. In all these classes of animals thread-cells 
were developed within the ectodermal coat of the animal, 
and in many, such as in 7. indivisa, each within a distinct 
and very apparent sac, and not in connection with the diges- 
tive system.* The type of structure, moreover, of the thread- 
cell in the Protozoon, the Hydro-medusa, the Annelid, and 
the Ctenophore, was essentially different for each class; and 
this fact alone would lead an observer to doubt as to the 
origin of the thread-cells of Eolis, which so exactly resembled 
those of the Hydro-medusz 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 apparatus 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 distinctive 
functions unimpaired; and he stated that his friend, Mr. Alder, 
one of the highest authorities on the Nudibranchi, still 
hesitated to assent to the doctrine sought to be proved by the 
present communication, on the ground of its extreme im- 
probability. He should therefore feel obliged to any of the 
members of the society or others who would lend their aid 
to the confirmation or disproof thereof. 
* This remark only applies to the Hydroids and their medusoids amongst 
the zoophytes. In the Actinie, Lucernarian Meduse, and Lucernaria, 
thread-cells are found in connection with processes of the endoderm, related 
to the reproductive apparatus. 
