102 



LOWER INVERTEBRATES. 



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Fig. 93. — Tentacular 

 knob of Agalmopsis. 



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onic tentacle and its characteristic side branches. The Physophora larva resembles 



the adult in all particulars, except size, and the presence of the last of temporary- 

 organs later to disappear in the growth of 

 the Agalma, viz., the embryonic tentacle. 



Several other genera of Physophores are 

 so closely allie"d to Agalma that they are 

 placed in the same family. One of the most 

 interesting of these is the genus Agalmopsis, 

 which differs from Agalma in its slighter 

 form and the intimate structure of its ten- 

 t;ioular knobs. Malistemma has also a pecu- 

 liar tentacular pendant which differs from 

 those of Agalma or Agalmopsis. 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-shai)cd and 

 dark crimson in color. At one extremitj^ it 

 is fastened to the inner walls of the involu- 

 crum, the free end bearing two terminal filar 

 ments and a vesicle. The various genera of 

 Agalmidffi differ in the character of this knob. 



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



only one terminal filament. Ilalistemma, 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 iStephanomia, a name which has been applied to 



genera of Siplionophora of widely different form, was given by 



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- 



phores 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 Ualistemma than of Agalma. It 



may be regarded as the type of the family Forskaliad^. 



One of the most beautiful genera of Physophoeid^ is the 



interesting animal known as Physophora, called in the dialect of the Messina fishermen, 



" Boguetti." Physophora is remarkable in possessing no polypstem, but in place of this 



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Fio. 94. — Agalmopsis picta,. 



