Zoological Society. 1 2 1 



movement but that which proceeded from the undulating movements 

 of the digitated extremities of the fins, as well as an occasional 

 slight twisting motion of the same organs. 



" I felt much interest in the beautiful display of a circulating fluid 

 on the dorsal surface of these animals, which was afforded me by 

 the assistance of a microscope. Through the semi-transparent mem- 

 brane of the back, a fluid could be readily perceived close to the sur- 

 face, evidently flowing in two directions, one taking a course down- 

 wards, and the other returning upwards; but I was unable to di- 

 stinguish two distinct vessels for these separate actions. 



" These animals seemed to be very torpid in their movements, 

 although sometimes, when floating upon the water, they would 

 be seen busily engaged in moving their fins about, but those actions 

 were soon suspended and their fins were suffered to hang lazily 

 down, as if fatigued with the short exertion, which did not move 

 them one inch about the glass of water ; and even when the little 

 indolent creatures did take the trouble to move themselves from one 

 side of the glass to the other, it was effected by a tardy motion, 

 stirring themselves first with one fin and then with the other, ac- 

 cording as circumstances might require. 



" I placed some small specimens of Porpita in the glass of water 

 containing the Glauci, to observe if they would attack them; for 

 some time one of the Glauci was close to a Porpita and was even 

 annoyed by the tentacula of the latter touching its back, yet the 

 Glaucus bore this, although with the usual characters of impatience, 

 yet without attempting to attack it. At last it seized the Porpita 

 between its jaws, and by aid of a powerful lens, an excellent oppor- 

 tunity was afforded me of closely watching the devouring process, 

 which was effected by an apparently sucking motion; and at this 

 time all the digitated processes of the fins were floating about, as at 

 other times when the animal was at rest; but I did not observe, in 

 one single instance, that they were of any use to the animal, either 

 to aid in the capture or to securely hold their prey when in the act of 

 being devoured ; for the animal seems to depend merely upon the 

 mouth in capturing its prey ; as in this and other instances, which 

 I had opportunities of observing, they seized their prey instantly 

 with the mouth, and held it by that power alone, whilst by a kind 

 of sucking motion the prey was devoured. The digitations may 

 therefore only be regarded as appendages to the fins to aid the ani- 

 mal perhaps in the direction of its movements, as it was observed 

 that they turned and twisted them about during the progressive mo- 

 tion, (that is, when this tardy animal is pleased to progress, which 

 appeared to me very rarely to meet with its inclination,) as if in some 

 way or other to direct the movements of the animal. 



" The Glaucus, after eating the tentacles and nearly the whole of 

 the soft under surface of its prey, left the horny portion, and re- 

 mained tranquilly reposing upon the surface of the water after its 

 meal, the only motion visible in the animal being the playing of the 

 digits of its fins. The mutilated remains of the Porpita sank to the 

 bottom of the glass. 



Third Series. Vol. 1 1. No. 65. Supplement, July 1837. R 



