16 



AC ANTHUS-ACARI. 



fishes. The common lancet fish is found chiefly in 

 the West Indian seas, where its flesh is much relished, 

 as being both wholesome and nutritious. The cha- 

 racters, and even the names, of the species are a little 

 confused. Some have the dorsal fin much pro- 

 duced ; others have the spines on the tail partially 

 concealed anteriorly by a tuft of bristles ; and others 

 again have the teeth so deeply grooved ou the one 

 side that their cutting edges resemble the teeth of a 

 comb. They are altogether a very curious genera of 

 fishes, peculiar to the tropical or warm seas, and very 

 characteristic of them, which are the only portions of 

 the sea where animals, whether fishes or reptiles, are 

 understood to graze the vegetable productions of the 

 deep. 



Acanthurus nigrricans. 



The above figure will give some idea of the shape 

 of these singular tenants of the deep, which, notwith- 

 standing their trenchant teeth, and the very formidable 

 weapons with which their tails are armed, cannot be 

 classed among predacious fishes. Their principal 

 food, at least that of most of the species, is not even 

 the small animals of the sea, but marine plants the 

 more succulent kinds of sea-weed, which grow so 

 abundantly in the shallows of the tropical seas. They 

 thus bear to the rest of the finny tribes a relation 

 somewhat similar to that which the herbaceous mam- 

 malia bear to the rest of that class. Not that they 

 ruminate ; but their intestinal canals are long, and 

 very much convoluted, as is the case in those of the 

 mammalia which live upon vegetable food ; and it is 

 not a little singular that the defensive weapons (for 

 it does not appear that they use the spines or lancets 

 for the purpose of attack) should be placed on nearly 

 the same part of their bodies. In the horse and the 

 ass, and still more remarkably in the giraffe and the 

 kangaroo, the defence is in the heels; and so powerful 

 is the kick in the giraffe, that if it take effect it can 

 fracture the skull of .the lion ; and the spines upon the 

 acanthuri are so situated that they deliver their blow 

 with the whole muscular power of the fish ; and thus 

 render it rather a serious matter for the sharks and 

 other voracious fishes to attack them in the rear. 



There is something analogous in another class of 

 the inhabitants of the sea the whales. The common 

 Greenland whale does not feed upon vegetable matter, 

 but its food consists of such small substances, and is 

 caught by so curious an apparatus the plates of 

 baleen, or whalebone and their fringes, that the animal 

 cannot either attack or defend itself from its enemies 

 by the mouth, or in any way with the forepart of the 

 body. But the blow which the common whale can 

 give with its tail is far more powerful than that even 



of the largest of the toothed whales ; and may be said 

 to bear nearly the same proportion to their bite that 

 the kick of the kangaroo bears to the bite of a dog, 

 or the kick of the giraffe to the bite of a lion. 



In these different situations of their weapons, which 

 may be traced through all the classes of animated 

 beings, we can discover a very striking proof of that 

 beautiful adaptation, equally free from redundancy 

 and defect, which makes the study of nature so useful 

 to us in the economy of our artificial contrivances. 

 All the predacious animals have their weapons in 

 front, and conducive to the purposes of feeding; and 

 the more powerful they are in preying, they have 

 their hinder parts weaker than the anterior ones 

 that is to say, weaker in proportion. Not only so, but 

 their eyes are turned more to the front, and infenced 

 and shaded by the superior parts of the orbits, so that 

 their most effective action is in guiding the animals 

 to their prey. The non-predatory ones, on the other 

 hand, have in general the hinder parts stronger in 

 proportion, so that they may defend the animals while 

 they are feeding ; and their eyes stand out, so that in 

 very many instances they can keep guard in the rear, 

 without turning the head. In the horse, the kangaroo, 

 and the giraffe, these adaptations are very striking, 

 and there is an approach to them in the acanthuri. 

 The form of the body, deep at the middle, but com- 

 pressed laterally, enables it to take a strong hold on 

 the water as a fulcrum ; while the comparatively slender 

 portion, near the root of the caudal fin, to which the 

 lancets are attached can move with great rapidity, 

 and the weapons cut right and left with great effect. 

 Their eyes, too, stand out; so that the fish can see its 

 enemy and take aim, instead of striking at random. 



ACANTHUS (Bear's Breech). A family of de- 

 ciduous herbaceous plants, containing seven species, 

 chiefly natives of the south of Europe. They belong 

 to the Linnaean class and order, Diih/nrni/ia Angio- 

 spcrmia ; Natural order, AcanthacecE. Generic charac- 

 ter : calyx of four unequal divisions, the two outside 

 ones being smallest ; the corona is of one lip ; stamens 

 four, two being longer than the others ; anthers unilo- 

 cular, and bearded ; capsuli oval, of two places, each 

 containing two seeds. The leaves of the A. mollis 

 are remarkably graceful, and are said to have supplied 

 Callimachus with patterns for the foliage of the capital 

 of the Corinthian column. The Arabs have a spe- 

 cies, the leaves of which they eat as a salad. 



ACARI (Cuvier, Leach). A class of the inver- 

 tebrate animals established by the late Baron Cuvier 

 of the great type annulata, or atnnifosa of Mac Leav, 

 the characters of which are as follows : Tracheae for 

 respiration ; body formed of but one segment : mouth 

 rostriform, in some furnished with maxillae and mandi- 

 bles ; legs six or eight : the following are the sections 

 and families of these so little understood and less 

 known animals, as but very few of the exotic species 

 have yet reached this country : 



Section I. Legs formed for walking. 

 A. Mouth with mandibles. 



Family I. TrombidiadcE : Palpi porrect, and fur- 

 nished at their extremities with a moveable append- 

 age. 



Eyes two, placed on a pillar. Body apparently 

 divided into tw r o parts by a transverse line; the 

 anterior division bearing the eyes, mouth, and four 

 anterior legs. 



Genus TrombitKum, Oci/pete. 



Eyes sessile. Body not divided by a' transverse 



