94 THE OCEANIC HYDROZOA. 



" The very large swimming bladder is distended with air," saj's this excellent observer^ 

 ' in such a manner that its longest diameter is horizontal. In all the species there may be 

 remarked at one end of the bladder a prolongation, also full of air, which is not provided with 

 suckers or prehensile filaments, and at whose surface, near the end, a distinct pit is perceptible, 

 which, as soon as the bladder is compressed, opens and allows of the exit of the contained air. 

 In some species this part cqnals half the entire length of the bladder, while in others 

 it is very short. The opposite end of the bladder, on the other hand, is, in all species, 

 covered on one side with suckers, which, in young individuals, are much more imperfect 

 than the others which lie in the middle of the vesicle. This end also possesses a pit on 

 its upper surface, which appears to be an opening of the bladder,^ and is in some species 

 provided with a particular solid process. Along the upper surface of the bladder there runs 

 a plaited ridge, which, in its common condition, is also filled with air ; but the animal can, at 

 will, press the air out of it, when the ridge collapses into a membranous fold, but the bladder 

 becomes thicker and more distended. 



" The bladder consists of a double membrane, an outer solid, and an inner much more 

 delicate one ; when the animal has lain in spirit, the inner membrane can be separated 

 from the outer as a separate bladder. 



" On the lower side of the bladder are the organs of nutrition, which consist of suckers 

 and prehensile filaments. The former arise either singly" from the bladder, or many 

 spring together from a common stem. The prehensile filaments are so far to be called 

 simple that they neither branch nor give off lateral offsets. They consist of a rounded 

 filament, which is covered throughout its whole length on one side with a series of reniform 

 acetabula (saug-warzen), and on the other side is supported by a narrow membrane, which 

 accompanies it from the root to the point. 



" At the root of each prehensile filament, of which there are many of different sizes on a 

 single animal, is a long, pointed receptacle of fluid (fliissigkeits-behalter), attached throughout 

 almost its whole length to the filament, and only free at its apex. The acetabula of the 

 prehensile filaments appear to be the organs which secrete the mucus which produces the 

 well-known urtication of tlie human skin, and by which animals which are seized are at 

 once paralysed." 



Eschscholz compares the receptacles at the bases of the tentacles to the ambulacral 

 vesicles of the EcMnodermata. 



After denying the justice of the statement of a Dr. Blume respecting the existence 

 of a nervous system in Phi/saUa, Eschscholz goes on to say : 



"That the PJii/salice have the power of emptying the air out of their bladder, and 

 so diving down, as the older writers relate (though their statements are only suppositions), 

 rests upon no direct observation. Flti/salicE which are touched, pricked, cut, irritated with 

 acrid substances, or placed in brandy, would certainly not fail to dive if they could, in order 

 to escape such treatment. But it is only by actual compression of the bladder that I have 



' This observation has not been verified by subsequent observers. 



" I entertain great doubts whether this is ever the case in adult Physalioi. Leuckart denies it 

 ill Ph. utricidus (' Ueber den Bau der Physalieu,' p. 195), which is in perfect accordance with 

 mv own observations. 



