REPORT ON THE SIPHONOPHOR^E. 17 



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part appears to act as an otocyst, since it is constricted off by a strong sphincter from 

 the wide palpon cavity, and forms a spherical terminal bladder in which a crystalline 

 otolith is kept in rotatory movement by a ciliated epithelium. Palpons are found 

 generally distributed in the Physonectss and Physalidae ; they are absent in the 

 Auronectse, Calyconectae, and Disconectae. Not unfrequently palpons are confused with 

 tentacles, as for instance repeatedly by Claus, even in Physo-phora. 



CYSTONS or ANAL VESICLES. 



Under this title I distinguish from the other polypoid organs of the Siphonophorae 

 certain vesicular sacs, which have hitherto been generally confused with the palpons. 

 They are indeed very like the latter, but are very essentially distinguished from them 

 by a terminal aperture. By means of this aperture, which the animals can open or 

 close at will, fluid and excretions are emptied from the canal-system, and water may also 

 be taken in. It is therefore to be regarded as an anus. The distal portion of the 

 cystons is frequently pigmented and furnished with special glandular cells, they also 

 sometimes contain definite crystalline excreta. These anal vesicles obviously stand in 

 closer morphological and physiological relations with the siphons than with the palpons ; 

 they are, however, distinguished from the former by the simple structure of the wall. 

 I find these excretory structures widely distributed among the Physonectse, but they 

 appear to be altogether absent in the other orders. 



TENTACLES or CAPTURING FILAMENTS. 



(Senkfdden, Stinging Filaments, Tentacular Filaments, Nematozooids.) 



Tentacles are present in all Siphonophorae, and are both as capturing organs and as 

 offensive and defensive weapons quite indispensable. Recent reports of their absence in 

 some species are certainly to be explained by the ease with which the delicate threads 

 are during capture detached from their base. The poly-person theory regards the 

 tentacles as independent polypoid persons. I agree, on the other hand, with the poly- 

 organ theory, which explains them as organs of the siphons. In my opinion the 

 tentacles of the two legions of the class are in their nature entirely different. In 

 the Disconanths (or Porpitariaa) the primary circle of tentacles on the umbrellar margin 

 of the medusoid larva (Disconula = Archimeda) persists ; there are at least eight present ; 

 their number usually becomes much increased ; they have no individual relations to 

 the separate siphons which bud forth in large numbers from the subumbrella. It is 



(ZOOL. CHALL. EXP. — PART LXXVII.— 1888.) Hhlib 3 



