200 ZOOPHYTA HELIANTHOIDA. 



which the support depends being converted into stone by a de- 

 position of calcareous matter in their texture, — the corium in 

 this manner becoming a sohd polypidom, and the muscular leaf- 

 lets partitions of limestone.* 



When a Helianthoid Polype is at rest and unalarmed, it can 

 dilate the body to fully twice its ordinary bulk by imbibing water 

 through the mouth or tentacula,-f- the bases of which open in 

 the spaces between the perpendicular lamellae. These spaces 

 being filled, the water is then made to permeate the rim of 

 the oral disk, which is full of cavities and cells for its recep- 

 tion ; and the tentacula are in the same manner distended, the 

 water being forced into them from behind while the little open- 

 ing on their tips is held close. The whole animal is thus dis- 

 tended to a wonderful degree, and every organ stretched and 

 displayed;— the tentacula spread out in quest of prey, — the 

 skin rendered almost clear from very fulness ; and the stomach, 

 pushed beyond its natural bounds, lies over the sides in swol- 

 len diaphanous lobes. The water thus introduced is doubtless 

 subservient to the purposes of respiration, and to aid this, the 

 vermiform filaments, and the internal surface of the stomach 

 and tentacula are clothed with vibratile cilia, exciting and di- 

 recting currents over the surfaces.:}: Since too the contents of the 

 stomach must be fully exposed to the influence of the water, the 



" " Dans cette classe d'animaux, le polypier ou la partie solide qui reste quaiid 

 le partie animale a ete dessechee et enlevee, est done une sorts de reseau calcaire 

 d"un tissu plus ou moins compacte, qui remplissoit les mailles, les vacuoles de 

 celle-ci. La proportion de ces deux parties est en rapport avec I'age du zoan- 

 thaire : plus il est jeune, plus il y a de matiere animale ; plus il est age, et plus 

 il y a de matiere inorganique : aussi la base de ces polypiers, le plus souvent 

 morte, est-elle fort dure, tandis que le sommet ou les bords essentiellement vi- 

 vans sont entierement mous." Blainville, Actinolog. 311 — See also Harvey in 

 Mag. Nat. Hist. n. s. 1. 474. 



•f " It has not, so far as I know, been clearly shevra by which of the com- 

 municating orifices the water enters. Though I took considerable pains, I have 

 not been able satisfactorily to ascertain this point ; I may remark, however, that 

 I have repeatedly noticed water entering at the mouth." Sharpey in Cyclop. 



Anat. and Phys. i. 614 Delle Chiaje asserts that it enters by the tentacula. 



Bull, des Sc. Nat. xvii. 471. He adds, " II est curieux d'observer le courant 

 d'eau qui, lorsque T Actinic se relache, penetre par quelques tentacules, et des 

 qu'elle se contracte, sort par d'autres tentacules precisement opposes aux pre- 

 miers. Ce phenomene s'observe sur toutes les especesd'Actinies." 

 ^ Sharpey in lib. cit. i. 614 — 15. 



