102 



L WER IN VER TEBRA TES. 



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onio tentacle and its cliaracteristic side branches. The Physoijhora larva resembles 



the adult in all jsarticulars, except size, and the ijresence of the last of temporary 

 organs later to disappear in the growth of 

 the At/alnia, viz., the embryonic tentacle. 



Several other genera of Physophores are 

 so closely allied to Agalma that they are 

 placed in the same family. One of the most 

 interesting of these is the genus Affalmojisis, 

 whicli differs from Agcdma in its slighter 

 form and the intimate structure of its ten- 

 tacular knobs. Ilalisteiivna has also a pecu- 

 liar tentacular pendant which differs from 

 those of Agalma or Agalmojms. In the 

 adult knob of Agalma the following struc- 

 tures are found : 1, an involucrum ; 2, a sac- 

 culus ; 3, terminal filaments and vesicle. The 

 involucrum is a membranous sac which covers 

 tlie knob when the other parts are retracted. 

 The great mass of the knob is made up by 

 the sacculus, which is corkscrew-shaped and 

 dar-k crimson in color. At one extremity it 

 is fastened to the inner walls of the involu- 

 crum, the free end bearing two terminal fila- 

 ments and a vesicle. The various genera of 

 Agalmida; differ in the character of this knob. 



Agalmopsis has a sacculus and involucrum, but no vesicle, and 



only one terminal filament. JIalistemma, probably the type of 



another family, has no involucrum, while it possesses a spirally- 

 coiled sacculus and a single terminal filament. The genus 



Crystallodes has tentacular knobs like those of Agalma, and is 



by some authors made a species of this genus. It differs, how- 

 ever, from Agalma in the rigid nature of the axis, in the shape 



of the covering-scales, and in minor points in the anatomy of 



the nectocalices. 



The genus Stephanomia, a name which has been api)lied to 



genera of Sii>honophora of widely different form, was given Ijy 



the elder Milne-Edwards to a Physophore in which there are 



many series of nectocalices appended to the nectostem. ^S*. con- 



torta is one of the most beautiful and graceful of all the Siphono- 



[jhores as by the combined movement of its many swimming-bells 



it gaily swims along in the water. It is peculiar in this respect, 



that the polypites are mounted on a long peduncle, which also 



bears the covering-scales .and the tentacles. The tentacular knobs 



resemble more closely those of IJalistemma than of Agalma. It 



may be regarded as the tyjie of the family Foeskaliad.e. 



One of the most beautiful genera of Piiysophoeice is the ^°' ■—■oa>noj>sispic 



interesting animal known as P/ii/sophora, called in the dialect of the Messina fishermen, 



" Boguetti." Physoplwra is remarkable in jDossessing no jiolypstem, but in place of this 



Fig. 93. — Tentacular 

 knob of A(jatinopAis. 



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