SIGNIFICANCE OF CERTAIN LARV.E OF ECHINODERMS. 1/5 



same tendency to rearrange the ciliated bands into transverse cil- 

 iated rings which is found among the holothurians. The outline 

 of the pluteus is shown in Fig. 7. When the developing ophiurid 

 has become quite large and the tissues of the pluteus are being 

 absorbed, the ciliated bands of certain of the arms become applied 

 to the disc in a quite definite manner, viz., about the madreporic 

 interradius which had an anterior position in the larva, a com- 

 plete ring is formed ; an interrupted ring is laid down between 

 rays 5 and 4 on one side and I and 2 on the other. A third 

 ring crosses the base of ray 3. Not until I had examined a 



H 



FlG. 7. Ophiuran pluteus (sp.? ) from the "tow" at Beaufort. 

 mouth. H, hydroccele. Ciliated bands stippled. 



A, anus; JIS, 



number of these metamorphosing plutei was I satisfied that this 

 arrangement of the ciliated areas was not accidental but in all 

 cases examined (a dozen or more) the arrangement was practi- 

 cally the same as that shown in Fig. 8. 



Echinoids. 



During the summers of 1900, 1901 and 1902 I succeeded in 

 rearing large broods of the larvae of Mellita tcstndinata from the 

 fertilized egg to the form in which the adult structure is attained. 

 The larva is a typical highly specialized pluteus as will be seen 

 from the outline of Fig. 9. The just metamorphosed Mcllitas all 

 showed three parallel transverse ciliated rings ; the middle one 

 of which is interrupted by the mouth (see Fig. 10). The func- 

 tion of these ciliated rings in the young Metlitas is probably to 



