OSTREAD.E.— THE PECTEN.— SEA-UKCHIXS. 



Biilijected to the test of other sieves with smaller holes, 

 and are classed according to their eize and worth. 

 The whole are then threaded on differently coloured 

 Eilk ; and in this way, assorted according to their 

 size and colour, are exposed for sale. 



We proceed to notice some other varieties of Ostrecuhv. 



The Scallop-shell (Peclen), so called because they 

 were worn in their hats by the medieval pilgrims, is 

 round, nearly equal-sided, and resting on the right 

 valve, wdiich is more convex, and distinguished by 

 numerous radiating ribs. Their channelled edges and 

 surfaces bear some resemblance to the teeth of a comb, 

 whence their scientific name, Pectm. 



Towards the summit the shell terminates in a 

 straight line, forming a kind of triangular appendage, 

 called the ear, to which the hinges are attached. 

 'J'hough the valves are very regular, they do not 

 resemble one another. In some species, whose shell 

 is closely shut, the lower valve is more or less convex 

 than the upper one. In others, both valves are convex. 

 The hinge is without teeth, and the ligament, by 

 which the shell is closed, is let into a triangular 

 depression, or "dimple." The retractile muscle is 

 unequal, and located nearly in the centre. Some- 

 times the edges are smooth, as in the Watered 

 Pecten {P. pseudamussium); but more frequently they 

 are arranged in strips or scales, as in the Smooth- 

 shelled Pecten (P. glaher). 



Other species, remarkable for elegance of form and 

 beauty of colouring, are :— The Ducal Mantle [Pecten 

 palliutn), the Coral Pecten, tlie Tiger Pecten, the 

 Purple Pecten, the Foliaceous Pecten, and the Northern 

 Pecten. Upwards of a hundred species are known and 

 have been described, of which twenty (including the 

 exquisite P. opcrcularis) inhabit the European seas. 



On the Mediterranean shores and along the coast of 

 the Atlantic the genus Peclunailus are abundant. The 

 shell is round and robust, and the animal inhabiting it 

 is also round and compact, with a large thick mouth, and 

 double branchiiB. 



The genus Spoiubjlus are remarkable for the rich 

 colouring of their shells, and their elegantly varied 

 forms. They are thick and solid, with unequal adher- 

 ent valves that are strongly covered with spines. 

 Their tenants in some respects resemble the oyster, 

 but more closely the pecten. Two rows of tentacles 

 fringe the edges of the mouth ; the exterior row being 

 frequently furnished at their extremities with coloured 

 tubercles. The most interesting species are Sponchjlus 

 regius, Spondylus radians, Spondylus avicidnris, 

 Spondylus crassisquama, ai}d Spondylus imperialis. 



We have also the genus Malleus, or Hammerhead, 

 included in the family of Ostreada;. The shell bears 

 some resemblance to the implement from which it 

 takes its name. The valves are blackish, nearly equal, 

 somewhat rugose on the outer surface, and on the 

 inner often brilliantly nacred. Being enlarged on either 

 side of the hinge, the prolongation gives them an 

 outline not unlike that of the head of a hammer; and 

 as they grow in a direction opposite that of the hinge, 

 the exteti&ion is not unlike its handle.* 



• Thi'se resemblances are particularly noticeable in tbe spccif.s 

 •Icsciibed by Larnaick, and named Malkus alba. 



Only twelve s[)ecios of this genus are known, and 

 these inhabit the Australian seas, and the Pacific and 

 Indian Oceans. 



Sea Urchins lodged in the rocks they have excavated. 



Michelet represents this strange product of tlie ocean 

 as nanating bis life-history in the following graphic 

 language : — " I was born without ambition. I crave 

 none of tbe splendid gifts possessed by those brilliant 

 gentlemen, the Molluscs. I have no desire to be con- 

 verted into mother-of-pearl or pearls ; no longing have 

 I for lustrous colours, a luxury of ornament which 

 would render me fatally conspicuous ; still less do I wish 

 for the grace of your volatile Medusas, the undulating 

 charm of whose shining locks attracts observation and 

 exposes one to calamity. mother Ocean 1 I desire 

 but one thing only : to be — to exist without these 

 external and compromising appendages ; to be thick- 

 set, robust, and globular, the shape in which I shall be 

 the least exposed ; in fine, I would remain a centralized 

 being. I have very little instinct for travel. It is 

 enough for me to roll occasionally from the surface- 

 waves to the bottom. Firmly adhering to my rock, I 

 could then resolve the problem of safety, whose solution 

 is vainly sought by your future favourite — Man. To 

 shut out all enemies, and admit all friends — especially 

 air, light, and water — would, I know, cost me a certain 

 degree of labour and a continual effort. Covered 

 with movable spines, I shall be avoided by my foes, 

 who, while I bristle like a bear, will call me a 

 sea-urchin.''* 



The structure of this remarkable organism, so admi- 

 rably adapted for its peculiar functions, is deserving of 

 the minutest examination. We may imagine it built 

 up in something like the following manner: — A globu- 

 lar hollow box, to use Mr. Gosse's expression, must 

 first be made — a globular hollow box, about three 

 inches in diameter, wiih sides scarcely thicker than 

 a wafer, formed of unyielding limestone, and yet 

 curiously fitted for the reception of the soft tender 

 parts of an animal which, at all periods of its existence, 

 completely tills the interior; a globular hollow box, 

 moreover, which will never be cast off or renewed, 

 which must hold the urchin in its old age as in its 

 infancy.^The limestone can only increase in size liy 

 being deposited ; and as all the vascular tissues are 

 concentrated within, they must deposit their particles 

 on the interior walls. It is true that this thickening of 

 the sides or walls from within necessarily diminishes 

 the size of the cavity, while, on the other hand, the 

 animal's incessant demand is for space, more space. 

 Day by day it feeds, it assimilates its food, it fattens 

 and expands; it needs a larger bouse, or cribbed, 

 cabined, and confined, it will perish ! 



IIow is the dilliculty to be conquered? By an 

 arrangement wdiich, like everything else in this world 

 of ours, demonstrates the infinite wisdom of the Creator. 

 The globular hollow box of the sea-urchin is not made 

 in one piece, in ten pieces, or in a hundred ; but it 

 is composed of six liundred pieces, all so accurately 

 • Jlicliclet, La Mcr. 



