CRISTATELLA. B\ 



CHAPTER VI. 



LUNATE ASCIDIAN ZOOPHYTES.-CRISTATELLA, ALCYONELLA, PLUMATELLA. 



By the general dispositions of Nature, the form of the active organic 

 portion of most zoophytes admits of comparison to a flexible funnel — one 

 of variable dimensions and capacity, through the influence of a number of 

 ribs — the tentacula. These important organs are endowed with many fa- 

 culties — so many, indeed, that some of them cannot be confidently ex- 

 plained. They are enabled to attract, seize, and to transmit the matter 

 necessary for sustenance of the hydra downwards to a central orifice con- 

 stituting the mouth ; and such currents are produced in the water as con- 

 duce to the renovation of the aerial fluids, essential for preserving its 

 salubrity. The food is conveyed to the stomach, where, by elimination 

 and assimilation, that portion which is required for subsistence and incre- 

 ment of the subject is withdrawn and incorporated with the system. 



From the wonted arrangement of the external parts, there are some 

 noted exceptions, of which, the first to come under review, is the form and 

 position of what, in the more perfect animals, would be denominated 

 the head. There the disposition of the prehensile or active organs 

 securing the food, is not in circular order, though alike vigorous as the 

 others in discharging their important functions. Instead of springing 

 from a circular lip, they issue as an entire marginal border from around 

 the edge of a fleshy horse-shoe or crescent. 



Thus, the hydra: of the zoophytes to fall under consideration, are of 

 a lunate, not of a circular ox funnel form. 



None of this precise description, however, in as far as I am aware, 

 belong to Scotland, as existing in a simple state. All are compound. 

 They are combined with a fistulous, arborescent, or gelatinous inorganic 



