PHYSALIA. 97 



them merely as ducts for conveying a (hypothetical) acrid fluid from a (hypotlietical) 

 poison-gland. He also controverts M. Lesson's opinion that certain of the colourless 

 tentacles arc to be regarded as branchiae; being quite sure that there is no difference 

 between these and the ordinary tentacles, except in the absence of colour. As regards 

 the function of the cyathiform bodies, he has no other than analogical evidence to offer. 

 The only organs in the Aculcphce with which he conceives them to have any resemblance are 

 the natatorial organs of the Thysojihora. But their little adaptation to a similar purpose, and 

 the entire absence even of their rudiments in young Phijsal'ue, discourage this comparison ; 

 while, on the other hand, they bear a singular resemblance to the female generative organs of 

 a DipJii/a, and this resemblance extends even to the younger stages of both. 



" Mr. Huxley concludes by referring Physalia to the position assigned to it by Eschscholz 

 among PliysojjJiorce, and near Biscolahe or Angela. In fact, he regards Physalia as, in all its 

 essential elements, nothing but a Plnjsopliora, whose terminal dilatation has increased at 

 the expense of the rest of the stem, and hence carries all its organs at the base of this 

 dilatation. 



" The paper was illustrated by pencil drawings of the structures described." 



In 1851, Professor Leuckart published a very valuable essay, 'On the Structure of the 

 PliysalicB and of the Siphonophorce in general,' which contains some important additions 

 to our knowledge of the structure of these animals. On one or two points, respecting which 

 Leuckart's observations are more complete than Von Olfers' and my own, I will quote him at 

 length. 



" The crest is an integral part of the outer wall of the body, and may be regarded as a 

 duplication of it. Between its two lamelliE there remains a cavity, which is not continuous 

 through its whole length, being divided by a number of transverse septa, which are visible 

 even from without, into a corresponding number of csecal chambers or compartments. 



"These septa are especially formed by the inferior muscular layer of the wall of the 

 body, whose elements here consist of large, trabecular, transverse fibres, composed of 

 fine fibrillse. 



" The length of the septa is very different, and they are alternately larger and smaller. 



"According to these differences, four groups of septa may be distinguished. The first 

 group contains the longest, which traverse the whole height of the crest, from its ridge to its 

 base. Of such septa I count six in the present species, a number which, notwithstanding the 

 difference in size (I examined individuals of two to three and a half inches in length) of 

 the body, appeared to be constant.^ These six septa divide the cavity of the crest into seven 

 successive chambers. Each such chamber is divided in the middle by a septum of the 

 second order, which extends from the ridge half-way down. In this way fourteen chambers 

 are formed in the upper part of the crest, and this number is increased by further repetition 

 of the dichotomous division to twenty-eight and fifty-six. The last septa are the shortest, 

 being little more than constrictions of the outermost ridge of the crest. 



" The position of the crest is commonly stated to be on the upper surface of the bladder. 



' Leuckart adds in a note : " Tliis character would, therefore, seem to be not without importance 

 in distinguishing species. In Ph. urctlmsa I counted twelve such scpt;i, witli wliicli the statements and 

 figures of Von Olfers agree." 



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