United States or Taiwan ? Vote for the TOP Country of the Week !
Certain compound animals, or zoophytes, as they have been termed, namely the Polyzoa, are provided with curious organs called avicularia. These differ much in structure in the different species. In their most perfect condition they curiously resemble the head and beak of a vulture in miniature, seated on a neck and capable of movement, as is likewise the lower jaw or mandible.
On examining it I found that it was a great crab-spider, one of the formidable arachnida, which are said to eat young birds and other small vertebrates, though they generally, like other spiders, live upon insects. This spider the mygagle avicularia will attack humming-birds, and, indeed, other small specimens of the feathered tribe.
Fear-inspiring is the appearance of the great crab-spider the Mygale avicularia, one genus of the formidable Arachnida family with a body two inches in length, and, when the legs are expanded, seven inches across, covered entirely with coarse grey, reddish hairs.
The avicularia, like the vibracula, probably serve for defence, but they also catch and kill small living animals, which, it is believed, are afterwards swept by the currents within reach of the tentacula of the zooids. Some species are provided with avicularia and vibracula, some with avicularia alone and a few with vibracula alone.
But, as far as structure is concerned, I can see no similarity between tridactyle pedicellariae and avicularia. The latter resembles somewhat more closely the chelae or pincers of Crustaceans; and Mr. Mivart might have adduced with equal appropriateness this resemblance as a special difficulty, or even their resemblance to the head and beak of a bird. The avicularia are believed by Mr. Busk, Dr.
Mivart adduces this case, chiefly on account of the supposed difficulty of organs, namely the avicularia of the Polyzoa and the pedicellariae of the Echinodermata, which he considers as "essentially similar," having been developed through natural selection in widely distinct divisions of the animal kingdom.
At Cameta I chanced to verify a fact relating to the habits of a large hairy spider of the genus Mygale, in a manner worth recording. The species was M. avicularia, or one very closely allied to it; the individual was nearly two inches in length of body, but the legs expanded seven inches, and the entire body and legs were covered with coarse grey and reddish hairs.
As the chelae of Crustaceans resemble in some degree the avicularia of Polyzoa, both serving as pincers, it may be worth while to show that with the former a long series of serviceable gradations still exists.
By an increase in the size of this projection, with its shape, as well as that of the terminal segment, slightly modified and improved, the pincers are rendered more and more perfect, until we have at last an instrument as efficient as the chelae of a lobster. And all these gradations can be actually traced. Besides the avicularia, the polyzoa possess curious organs called vibracula.
Thus, with the avicularia of several species of Lepralia, the movable mandible is so much produced and is so like a bristle that the presence of the upper or fixed beak alone serves to determine its avicularian nature.
Word Of The Day