4io 



THE CIRRIPEDS, TUNICATES AND ECH1NODERMS. 



The Metamorphosis. In the cirripeds the larval cephalic shield is usually 

 very large and the body lies on its concave neural surface. Its margin is sensitized 

 and drawn out into very prominent horns or lobes, of which there are usually two 

 especially long ones in front, two behind, and minor ones between. (Fig. 289.) 

 After a time the caudal lobe elongates, the antennae migrate forward and haemally, 

 and the thoracic appendages and the rudimentary lateral eyes make their ap- 

 pearance. 



The larva, having taken on the shape and general appearance of an ostracode 

 (cypress stage) which it will be recalled is one of the first forms to make its appear- 



oc 



ov. 



FIG. 275. Semi-diagrammatic sagittal section of a cirriped. Lepas, 



FIG. 276. Mouth parts of Lepas. 



ance in the geological record, attaches itself to some foreign object, haemal side 

 down, by glandular, disc-like expansions of its first pair of appendages. (Fig. 

 274.) Cement glands appear and the greatly enlarged cephalic outgrowth be- 

 comes firmly attached. The body next turns completely over; the stalk elongates, 

 carying with it the remnants of the first pair of appendages, and the animal grad- 

 ually takes on the adult form. (Figs. 274, 275.) 



Appendages. Eleven pairs of appendages may be represented; two pairs 

 of antennae, three pairs of jaws, including the mandibles, and the first and second 

 pairs of maxillae, and six pairs of abdominal appendages. With the metamor- 

 phosis there is a strongly marked tendency toward the reduction, or atrophy of 

 many important larval organs. All of the eleven pairs of appendages present in 

 the larvae are never fully developed in the later stages. Even in the least modified 

 forms, the two pairs of antennae are either greatly reduced or absent; the three pairs 

 of jaws or oral appendages are very small, and two or three pairs of the six pairs of 

 abdominal appendages may be absent. Only nine pairs are present in the alcip- 



