BIVALVED SHELL-FISH. 



375 



animal has taken too great a quantity of water, 

 it is seen to spurt it out of its hole with some 

 violence. Upon this seemingly thin diet it 

 quickly grows larger, and soon finds itself 

 under a necessity of enlarging its habitation 

 and its shell. The motion of the pholas is 

 slow beyond conception ; its progress keeps 

 pace with the growth of its body ; and, in 

 proportion as it becomes larger, it makes its 

 way farther into the rock. When it has got 

 a certain way in, it then turns from its former 

 direction, and hollows downward ; till at last, 

 when its habitation is completed, the whole 

 apartment resembles the bowl of a tobacco 

 pipe; the hole in the shank being that by 

 which the animal entered. 



Thus immured, the pholas lives in darkness, 

 indolence, and plenty ; it never removes from 

 the narrow mansion into which it has pene- 

 trated ; and seems perfectly content with 

 being inclosed in its own sepulchre. The 

 influx of the sea-warer that enters by its little 

 gallery satisfies all its wants ; and, without 

 any other food, it is found to grow from seven 

 to eight inches long, and thick in proportion. 



But they are not supplied only with their 

 rocky habitation ; they have also a shell to 

 protect them : this shell grows upon them in 

 the body of the rock, and seems a very 

 unnecessary addition to their defence, which 

 they have procured themselves by art. These 

 shells take different forms, and are often com- 

 posed of a different number of valves ; some- 

 times six, sometimes but three ; sometimes 

 the shell resembles a tube with holes at either 

 end, one for the mouth, and the other for void- 

 ing the excrements. 



Yet the pholas thus shut up, is not so soli- 

 tary an animal as it would at first appear ; for 

 though it is immured in its hole without egress, 

 though it is impossible for the animal, grown 

 to a great size, to get out by the way it made 

 in, yet many of this kind often meet in the 

 heart of the rock, and like miners in a siege, 

 who sometimes cross each other's galleries, 

 they frequently break in upon each other's 

 retreats. Whether their thus meeting be the 

 work of accident or of choice, few can take 

 upon them to determine : certain it is, they 

 are most commonly found in numbers in the 

 same rock ; and sometimes, above twenty are 

 discovered within a few inches of each other. 1 



1 Molluscae. Mzfhy may have probably noticed, in 

 their ramblings along the sea beach, certain gelatinous 

 transparent masses deposited by the receding tide upon 

 the sands. They resemble very large planoconvex lenses, 

 and are devoid of colour, except in a few minute points, 

 which appear like grains of yellow sand, or the eggs of 

 some shells embedded in their substance. This has led 

 many to consider them as the spawn of some marine ani- 

 mal. If one of these jellies be placed in a tub of brine 

 immediately after it reaches the shore, the observer, will 

 be surprised to find it possessed of animation. The su- 



As to the rest, this animal is found in great- 

 est numbers at Ancona r in Italy ; it is found 

 along the shores of ^Tormandy and Poitou, in 

 France ; it is found also upon some of the 

 coasts of Scotland : and, in general, is con- 

 sidered as a very great delicacy at the tables 

 of the luxurious. 



perior, or convex part, will expand like the top of an 

 umbrella, and from its under surface several fringed and 

 leaf-like membranes will be developed. The remains 

 of numerous threads, or tendrils, will float out from the 

 margin of the umbrella, following the motions of the ani. 

 mal as it swims around the tub. These threads are often 

 several feet in length before they are broken by the sand; 

 they are probably employed both to entice and secure the 

 prey, and they produce a sharp, stinging sensation, when 

 applied to the skin. It is from the appearance and offen- 

 sive power of these last organs, that seamen have given 

 the animal the title of the sea nettle, and naturalists the 

 generic name Medusa. 



The medusa is a familiar example of the class of 

 animated beings which are the subjects of the following 

 remarks. They are all alike gelatinous and transparent, 

 and many of them melt and flow away when exposed in 

 the open air to the direct rays of the sun. 



' Of all the tribes of molluscae which are scattered over 

 every part of the ocean, the most splendid and the best 

 known is the Portuguese man-of-war (Physalia). This 

 is an oblong animated sack of air, elongated at one extre- 

 mity into a conical neck, and surmounted by a mem- 

 braneous expansion running nearly the whole length of 

 the body, and rising above into a semicirclar sail, which 

 can be expanded or contracted to a considerable extent, 

 at the pleasure of the animal. From beneath the body 

 are suspended from ten to fifty or more little tubes, from 

 half an inch to an inch in length, open at their lower ex- 

 tremity, and formed like the flower of the blue-bottle. 

 These have been regarded as temporary receptacles for 

 food, like the first stomach of cattle ; but as the animal 

 is destitute of any visible mouth or alimentary canal, and 

 as I have frequently seen fish in their cavities apparently 

 half digested, I cannot but consider them as proper stom- 

 achs ; nor indeed is it a greater paradox in zoology that 

 an animal should possess many independent stomachs ; 

 than that the strange carnivorous vegetable, the saraciriea, 

 should make Use of its leaves apparently for a similar 

 purpose. From the centre of this group of stomachs 

 depends a little cord, never exceeding the fourth of an 

 inch in thickness, and often forty times as long as the 

 body. The size of the Portuguese man-of-war varies from 

 half an inch to six inches in length. When it is in mo- 

 tion, the sail is accommodated to the force of the breeze, 

 and the elongated neck is curved upward, giving to the 

 animal a form strongly resembling the little glass swans 

 which we sometimes see swimming in goblets. 



The mode in which the animal .secures his prey has* 

 been a subject of much speculation, for the fish and crabs 

 that are frequently found within the little tubes are often 

 large enough to tear them in pieces could they retain 

 their natural vigour during the contest. Deceived by the 

 extreme pain which is felt when the cable is brought into 

 contact with the back of the hand, naturalists have con- 

 cluded, I think too hastily, that this organ secretes a poi- 

 sonous or acrid fluid, by which it benumbs any unfortu- 

 nate fish or other animal that ventures within its toils, 

 allured by the hope of making a meal upon what, in its 

 ignorance, it has mistaken for a worm. The secret will 

 be better explained by a more careful examination of the 

 organ itself. The cord is composed of a narrow layer of 

 contractile fibres, scarcely visible when relaxed, 011 ac- 

 count of its transparency. If the animal be large, this 

 layer of fibres will sometimes extend itself to the length 



