GENERAL CHARACTERS OF CIRRHOPODA. 281 



continual vibration of which, currents are produced in the sur- 

 rounding water, that serve to bring food to the animal, and 

 a fresh supply of fluid for the aeration of the blood by means of 

 the gills, which are situated at the base of these appendages. In 

 this conformation, there is an evident analogy with many Crus- 

 tacea. Further, the mouth is furnished with lateral jaws, which 

 no Mollusca possess; and the Nervous System consists of a double 

 cord, with a pair of ganglia in each segment of the body, pre- 

 cisely as in the Articulata in general. The most interesting 

 proof, however, that the Cirrhopoda belong to this division, is 

 derived from the history of their development. On their liber- 

 ation from the egg, they present a form much more analogous 

 to that of some ofjhe Entomostracous Crustacea, than to that of 

 the adult animal, which they only acquire after a series of meta- 

 morphoses. 



893. The young animals, when just hatched, are of a nearly 

 globular, but somewhat depressed, form, with the carapace trun- 

 cated in front, and furnished with lateral horns, within which the 

 formation of the antennae appears to take place. They are also 

 provided with three pairs of limbs. As they change their skin, 

 their form gradually alters, and between the first and third moults, 

 the posterior points of the carapace and abdomen usually become 

 elongated into very long, spear-like processes. In their last 

 stage, the larvae are inclosed in a bivalve carapace, and closely 

 resemble the Cypris (Fig. 605) ; they then possess a pair of 

 eyes, and large four-jointed antennae, which are well furnished 

 with muscles. The third joint of these organs is prehensile, 

 being generally converted into a circular sucking disc, and they 

 are employed by the little animal in attaching itself to various 

 bodies in the water, and even in walking. In course of time the 

 thorax gives rise to a little process bearing the antennas and eyes 

 at its extremity ; the animal then finally attaches itself by its 

 antennae to some object in the water, and pouring out a quantity 

 of a peculiar cement, from ducts running up from the body into 

 the antennae, becomes permanently fixed, when the above-men- 

 tioned process becomes elongated and converted into the peduncle 

 in those forms which are furnished with such an organ. By 



