366 The Structure and Habits of Physalia. 



These masses do not embrace the entire circumference of the 

 band, but only three sides as it were ; "the fourth being left free 

 along its whole length. It is in the thread capsules that the pecu- 

 liarly acute stinging power of the Physalidse resides ; although, 

 as yet, both the chemical composition and the mode of secre- 

 tion of the poisonous fluid with which the threads are embued, 

 is altogether unknown. It is almost certain, however, that the 

 extension and contraction of the tentacles is attributable to its 

 own muscular structure, and not to the injection of the poison- 

 ous fluid supposed by Lesson and others to be a secretion of 

 the basal saccular appendage already referred to. 



The extensile quality of the tentacle is very remarkable. 

 Thus I have repeatedly succeeded in winding it on a card by 

 merely placing the animal on a board during the operation, and 

 reeling off the thread, which, by this means, is reduced in 

 thickness to that of fine silk, and may be continuously wound 

 until it attains a length of eight or ten yards. This filament, 

 when dried in the sun, will keep for any length of time, and 

 forms a beautiful object for the microscope ; the fibrillse of the 

 muscular band and the crescentic bundles of thread-cells 

 being admirably seen, whilst their original colour is in nowise 

 destroyed. 



My endeavours to preserve the pneumatophore by drying 

 in the sun, were invariably unsuccessful for, although it re- 

 mained distended and its upper and lateral portions acquired 

 the tough consistence of a dry membrane, the setting in of de- 

 composition along the inferior fleshy portion always ended in 

 its rupture. Small specimens of the allied family of Velella, 

 however, which were preserved on glass slides by a similar 

 process of drying, in 1857, are still in my possession, together 

 with the delicate tentacles of Plrysalia just alluded to. 



Although there cannot be a doubt that nutritive organisms, 

 probably consisting of minute Entomostraca, Infusoria, or 

 Khizopoda, are seized after having been paralysed by the urti- 

 cating organs of the tentacles and polypites (for these bodies 

 also occur in the latter appendage), there is, I think, good 

 reason to suspect that Mr. Bennett, who describes the process 

 of fish capture by a Physalia, must have been misled as to the 

 cause and effect of what he witnessed, for the following reasons : 

 In a great number of cases the Physalia is accompanied by one 

 or more small fishes, precisely in the same manner that the 

 pilot-fish accompanies the shark. These fishes swim round 

 and round and through the depending tentacles without incon- 

 venience, and their association with Physalia is undoubtedly 

 one of choice, being in all likelihood due to the quest of some 

 kind of food which is attracted towards it, or furnished through 

 its excretions. I have so repeatedly witnessed this association, 



