22 



A C E P H A L A. 



very sharp, arc much more slender, and without any 

 notch in the mandibles. Their tarsi are weaker ; and 

 their claws, though very sharp, are much more slender 

 in proportion to the size of the birds. Their feet have 

 three toes in front and one behind ; but the outer toe 

 is generally capable of being reversed, so that the 

 toes act two against two, in clutching. Some of 

 them have erected feathers, or a sort of crests, 

 upon the sides of the head, which have procured 

 them the names of horned owls or sacred owls ; and 

 those which are without these crest feathers are called 

 smooth-headed owls. 



Though in general timid birds, preying in the 

 dark or the dusk, there are some of them of more bold 

 and powerful character, venturing abroad during the 

 day, especially in gloomy weather, and committing 

 considerable ravages upon birds and the smaller qua- 

 drupeds. These are, however, chiefly inhabitants 

 of northern and thinly inhabited or uninhabitable 

 regions ; and they rarely approach the dwellings or 

 the possessions of man, and cannot be said to do much 

 or material injury. 



From the nature of their food, which is chiefly the 

 different species of mice and other small and de- 

 structive quadrupeds, of which they capture vast 

 numbers, owls may be regarded as among the most 

 serviceable of wild birds ; and those species which 

 are of the greatest use are so far from timid or re- 

 tiring in their mariners, that they resort to farm-yards, 

 barns, and other places, and perform their services, 

 even in spite of the persecution which they meet 

 with from the thoughtless ; and were they encouraged 

 and protected in proportion to the usefulness and the 

 assiduity of their labours, there is no doubt, that they 

 might be made to add both to the value and the 

 interest of most parts of the country. For notices 

 of the species, see OWL. 



ACEPHALA (literally " having no head"). The 

 fourth in order of the six classes into which Cuvier 

 divides the Mollusca. (See MOLLUSCA.) The grand 

 character of the class, by which the whole of the nu- 

 merous orders, families, and genera, which are com- 

 prehended under it, are distinguished from all the 

 other mollusca, is that of having no visible head or 

 neck, the mouth being merely an opening in the com- 

 mon integument of the body, without jaws, teeth, or 

 any hard parts whatsoever. They are also without 

 organs of sight or hearing, or indeed any allocated 

 parts which we can pronounce to be organs of any 

 sense ; so that we can say nothing about the extent 

 or the kind of their sensations. The mouth is situated 

 under the cloak, or in its duplicature ; the cloak being, 

 in the majority of cases, double, and folded over the 

 body, sometimes with the lobes free for their whole 

 length on the under part ; at other times united in the 

 posterior part, so as to form a tube ; and at others, 

 again, united for the greater part of its length. Their 

 organisation is very simple, there being, in many of 

 the species, very little distinction of gullet, stomach, 

 and intestinal canal, but merely one continuous tube, 

 which has few convolutions. Their nervous system is 

 equally simple, consisting of one ganglion situated on 

 what may be considered the gullet, and generally 

 two further down ; but these last, as well as the cord 

 by which they are united to the first one, are often so 

 obscure that they can hardly be traced. They are all 

 understood to be self-fertilising, as well as bisexual ; 

 but still, production is no more spontaneous in them, 

 than in those animals which have the sexes in separate 



individuals. A single individual can, however, soon 

 stock a considerable space with them, as, under fa- 

 vourable circumstances, they are very prolific. They 

 are all inhabitants of the \v;t(cr ; and indeed few or 

 none of them have sufficient powers of locomotion for 

 finding their food upon land. Some adhere to the 

 rocks by peduncles or stalks ; others are chained by 

 byssi, or threads ; some make use of these threads 

 for motion ; others move by means of the foot along 

 the surfaces of rocks and other substances ; others 

 effect a leaping motion by suddenly shutting the 

 valves of their shells ; and others, again, make their 

 way through the water by compressing their bodies 

 and ejecting a jet against the water in the rear. 

 Many are incapable of quitting the bottom of the 

 water ; and others bore into the mud, or rocks. 



They are, as has been said, very numerous ; and 

 are also exceedingly varied in their sizes, forms, 

 and habits. Some, as the genus C'/iama, are among 

 the largest, if not the very largest, of invertebratcd 

 animals ; others are very minute. Some, as the oyster 

 family, are much sought after as food ; others, as the 

 various species vulgarly called pearl oysters or pearl 

 muscles (the Avicula margaritifcra of the Indian seas, 

 and the Unio margaritifera of many of the British 

 rivers, especially in the northern parts of the country), 

 are much esteemed for the pearls which they afford. 

 Some are equally mischievous, as the Teredo navalis, 

 which bores into the timber of ships, perforating it 

 till it has the appearance of a honey-comb. 



There is one circumstance attending this class, 

 which is more favourable to a useful knowledge of it 

 than any thing that is to be found in those tribes of 

 aquatic mollusca which have free range of the sea, 

 and can ascend and descend in the waters at their 

 pleasure. Of these, more especially of such as, 

 from the forms and qualities of their shells, we would 

 naturally infer to be the most interesting, hardly 

 any thing is known but the empty shells ; and the 

 history of these, however minute or perfect it may be, 

 bears about the same relation to the history of the 

 living animals, as a history of the costumes of dif- 

 ferent nations would bear to the history of those 

 nations themselves. It so happens too, that the uni- 

 valve pelagic shells, whether unilocular or multilo- 

 cular, that is, whether they consist of one chamber 

 or of many, which inhabit the depths of the ocean, 

 and, upon the general principle of all sea animals, are 

 not cast upon the shores till they are dead, are the 

 most striking in their forms and the most beautiful 

 in their colours. They are, therefore, those 

 which are most eagerly sought after to stock the 

 cabinets of the curious ; and the consequence has 

 been that, in as far as molluscous animals are covered 

 with shells, the science of them has become a science 

 of shells rather than a science of animals a peculiar 

 department of mineralogy rather than a part of 

 zoology. Now, as the acephala inhabit the banks 

 and bottoms at reachable distances, many of them 

 without low water mark, and none of them beyond 

 the reach of dredging (at least so far as is known), 

 they form a branch of this very interesting depart- 

 ment of nature, which can, to a very great extent, at 

 least, be studied zoologically; and the habits of the 

 animals themselves, as well as the mere forms of their 

 encasements, can be made matter of science. 



The acephala admit of a very convenient division 

 into two sections those which have shells, and those 

 which have not. The first of these are usually styled 



