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fixed sac or a floating polypite, is the gonozooid." The Gonotheca, 

 or chitinous capsule " within which the gonophores are produced," 

 is of coui'se a distinct structure. 



The Hydroid colony is then described, and here we find tlie 

 anatomy and physiology of the minute appendages fully explained. 

 The thread cells, with their retractile poisonous darts ; the palpocils 

 or sensitive hairs ; the nematophores, with their curious processes ; 

 the extensile filaments or fishing lines ; and the extraordinary 

 snake-like organs of the genus Ophoides, are especially interesting 

 to the microscopist ; and here he will find a concise account of 

 their minute anatomy, supposed functions, and observed actions. 



The following graphic description of the circulation is given in 

 this section: — 



"A stream, bearing along with it a multitude of restless gi-anules of various 

 sizes, issues from the stomachs of the polypites and rushes through the 

 cavity of the crenosarc, pervading every porti(m of the organism. After 

 flowing downward for some time, there is a pause in the circulation, and then 

 the current rushes back with great impetuosity, and once more entering the 

 stomachs of the polypites, mingles with the contents. A busy ferment takes 

 place for some seconds in the digestive sac, the larger particles hurrying to 

 and fro amidst the contained mass of food, until at length the efflux again 

 commences. The inner surface of the ca^nosarc is covered with vibratile cilia, 

 and these seem to be the chief agents in maintaining the flow of the currents." 



The section headed " Reproduction " is a most absorbing portion 

 of the work, and here again we find a full account of the microscopic 

 organs. 



In his description of the medusiform zooid or swimming polypite, 

 the author is quite enthusiastic. After minutely describing its 

 structure and functions, he says : — 



"It would be difficult to exaggerate in speaking of these floating flower 

 buds, as they may well be called. The vivid tints which they often 

 display, the gracefulness of their form, the exquisite delicacy of their 

 tissues, and the vivacity of their movements, combine to render them 

 singularly attractive. Frequently they are so translucent that their bubble 

 like forms only become visible in a strong light. In other cases the 

 umbrella is delicately tinted, while the manubrium displays the gayest 

 colours, and brilliant ocelli glitter on the I ulbous bases of the tentacles. 

 To their other charms that of phosphorescence is often added ; they 

 are not only painted like the flower, but at night they are jewelled with 

 vivid points of light, set round the margin of the bell, or one central lamp 

 illumines the little crystal globe, and marks out its course through th's water. 



Like miniature balloons they float suspended in the water for 



awhile ; then they suddenly start into motion, propelling themselves by a series 

 of vigorous jerks or casts, and at the same time contracting the tentacles into 

 the smallest compass ; then thej' become quiescent again, and sink slowly and 

 gracefully, like parachutes, to the bottom of the vessel, some of the arms 

 extended laterally, and the rest dependant. In all cases locomotion is 

 effected by the pulsation (alternate systoleanddiastole) of the swimming-bell." 



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