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'Eain and Dr Wright found a speci- 

 men of Eolis Landsburgii on Eudendrium rameum. Eudendrium 

 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 

 Goryne 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 G. 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 Allman 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 seticomis, 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. 



