80 



be formed of circular mviscles, press on tlie fluid contained 

 within the polype and force the weakest part, and consequent- 

 ly the creature ascends throiijih the mouth of the cell ; and 

 Dr. Farre thinks that the stomach has a power also of 

 lengthening itself, and so assisting the protrusion. But 

 whatever power produces it, the expansion is very gradual. 

 As the polype lies in the cell, it is drawn into an S configura- 

 tion, and thus may be said to be packed away in a very small 

 compass. It must not be supposed that all the structures 

 here mentioned can be viewed in a single specimen; it 

 requires a good microscope, good light, and repeated ex- 

 aminations; for at first all seems confusion. The poly- 

 pidoms of this order vary greatly in size, appearance and 

 structure. But although there have been reasons to consider 

 the solid parts of the foregoing orders as organic, an opinion 

 which is opposed by many, yet here their organic character 

 is allowed, and the point need not therefore be enlarged 

 OB. The solid parts are here properly considered to be 

 continuations of the external parts of the polype. 



The arrangement of the horny cells of the first family 

 varies ; in some they are arranged in parallel companies, 

 like Pan's pipes, in others in irregular clusters^ and in a few 

 they are without any definite order. 



With the exception of those genera forming the family 

 Vesiculariada?, already mentioned, the whole belonging to 

 this order are either calcareous or membrano-calcareous. 

 Those species forming the genus Crista bear a great re- 

 resemblance in form to the Sertularicc, among the HydroidcE ; 

 with which they were formerly associated. They are ar- 

 borescent, and the centre of the trunk, branches and cells 

 are occupied by a vital pulp, from which the polypes are 

 developed. The polypes are thus united into one compound 

 animal as in the iirst order. The growth of the polypidom 

 is also similar in these widely separated genera, and as 

 the reproduction is also by ovarian vesicles, nothing could 

 be more natural than associating them together, if external 

 characters alone were to be our guide; but the polype is 

 widely different. The terminations of the branches and 

 nevy cells are closed, but as developement advances the 

 cells open, in a precisely similar manner to what has been 

 noticed while speaking of the llydroidie. When the pulp has 

 eflected an advancement to the extent of an internode, it 

 stops for a short period, and what was semi-membranous and 

 pellucid becomes white and solid by the deposition of calca- 

 reous rwatler. But those parts which are niembranous and 

 pellucid while the creature is living, become after death 

 very solid and brittle, arising probably from the crystalization 

 of the calcareous particles, as soon as they are freed from the 



