PHYSALIA. 99 



M. De Quatrefages goes on to say, that, to account for this reappearance of the air, 

 we must suppose either that it is secreted, or that it enters by the pore, and he adopts 

 the latter hypothesis, conceiving that the walls of the air-vesicle are so strong and elastic 

 as to act like a perforated, hollow, caoutchouc ball, which yields its air when compressed 

 by the hand, and, expanding when the compression is removed, sucks it in again. The 

 muscular fibres of the body- wall act, in M. De Quatrefages' opinion, as the compressing 

 force, and when they are relaxed the vesicle resumes its primitive form. I must say 

 that this hypothesis appears to me to be quite inadmissible. The wall of the pneumatocyst 

 is, so far as my recollection serves, kept tense by the air which it contains, so that when 

 it is pricked or cut, the organ at once collapses, by its own elasticity, quite independently 

 of the muscular body-wall. And the extreme thinness of the membrane of the pneumatocyst 

 is, to my mind, incompatible with the notion that its elasticity is sufficient to overcome 

 the weight of the wall of the hydrosoma. 



As little can T agree in M. De Quatrefages' view of the functions of the air-vesicle, 

 which he supposes to be respiratory. A chemist, I think, would not lay much weight on the 

 two eudiometrical experiments whose results are given ; and the dense and tough, though 

 thin, elastic membrane of the pneumatocyst, covered as it is by the endoderm (tlie mucous 

 layer of M. De Quatrefages), is hardly the structure in which a physiologist can recognise a 

 special respiratory apparatus. 



On injecting a Phyaalia by one of the polypites, M. De Quatrefages made an observation 

 which seems to point to the existence of a system of canals in this Physophorid similar 

 to those which cover tlic upper surface of the pneumatophore in Velella and Porpita. 



"I saw that the coloured liquid had passed into a perfectly free cavity on almost 

 the whole of the lower face and a part of the sides of the body, but, beyond a certain limit, 

 this cavity seemed to me to become changed into an extremely close network' of canaliculi, 

 ascending even on to the upper face. Muscular (.'') bands passing from the parietes of 

 the body to the air-vesicle, properly so called, kept the two concentric bladders in connexion 

 and traversed the cavity. I regret not having ascertained if this last, or the 

 network, which is a prolongation of it, passed into the crest, but I am led to believe 

 it did so." 



I do not propose to discuss the histological details into which the author enters, 

 but I must remark that he has unfortunately confounded the tentacular sacs with polypites, 

 while he supposes the latter to be hepatic organs. The account of the development of 

 the polypites and of the reproductive organs is also, in many respects, imperfect. 



The perusal of the works of the various writers who have occupied themselves with the 

 establishment of specific distinctions among the Phi/salia;, simply makes one long for the 

 advent of a Caliph Oaiar in this department of zoological literature. A sort of unpleasant 

 vertigo is the only result I can report of my study of tlie systematic labours of Von Olfers, 

 Lesson, and Lamarck, but those who are inclined to take up the inquiry will find a very 

 elaborate discussion of the synonymy and characters of the various so-called species in the 

 already-cited memoir of the first named of these naturalists. 



Eschscholz, on the other hand, is, as usual, clear and intelligible, and, as his species are 



1 This network seems to have been first noticed by Tilesius. See Eysenhardt, 1. c., p. 414. 



