424 



THE CIRRIPEDS, TUNICATES AND ECHINODERMS. 



The apparent difference between them, therefore, is largely due to the absence 

 of chiten in one case and its presence in the other. 



The Larval Cephalic Appendages. The ciliated lobes of the echinoderm larva 

 must not be confounded with primitive appendages, with which they have nothing 

 in common. The true larval appendages appear in the same place as the cephalic 

 appendages of the nauplius, that is, on the neural side of the head in front of the 

 mouth, and in the angle between the lateral margin of the thorax and the preoral 

 lobe. (Figs. 290, 291, 292, c.a.p.} There appear to be two pairs; or at least when 



i E \^t cf ^ 



w^" 



r* 



FIG. 292. Star-fish larvas, seen as opaque objects, illustrating the mode of fixation and the metamorphosis. 



Semi-diagrammatic. 



they have attained their full development and have taken up their final position 

 on the projecting surface of the head, there are three appendages, an 

 unpaired one lying beyond the adhesive disc, and one on each side of it. (Fig. 

 291, c.a.p.) Each appendage is thick-walled and muscular, with a long basal por- 

 tion and a short terminal knob studded with small adhesive papillae. At this 

 time they greatly resemble the three cephalic appendages of a tunicate larva 

 (Figs. 284, 285), or the minute adhesive antennas of the cirripeds and parasitic 

 Crustacea. (Figs. 274, 278, 280, 283.) 



Attachment. The young star-fish larva is said to attach itself voluntarily 

 at first and for a short time only. Later it becomes permanently attached, head 

 first and neural side down, in the same remarkable manner as a young cirriped, 



