lO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 72 



Along the ambulacral grooves, except in most of the Comasteridse, 

 and usually also internally along the digestive tube, is a usually 

 regular row of little round bodies, conspicuously colored in preserved 

 specimens though usually colorless in life, called sacculi (fig. 4) which 

 remind one strongly of the glandular dots on the leaves and petals of 

 certain plants such as the species of Hypericacese. They are assumed 

 to be excretory organs. 



VIVIPAROUS CRINOIDS, AND SEXUAL DIFFERENTIATION 

 Three antarctic comatulids are viviparous, the young developing in 

 special pouches or marsupia formed on the pinnules in two, but on 

 the arms themselves in one. In all three of these the two sexes are 

 easily distinguished by superficial external examination. Besides 

 these three comatulids only six echinoderms are known to exhibit 

 sexual dimorphism, four irregular echinoids, one holothurian, and 

 one ophiuran. Excepting for one of the echinoids (AnocJianus) all 

 are from antarctic or subantarctic regions. 



THE DEVELOPMENT OF THE COMATULIDS 

 The early stages of the comatulid larvae are passed within the egg 

 membrane and the developing eggs usually hang from the bases of 

 the genital pinnules like little bunches of grapes. It is only after the 

 formation of the elements of the skeleton — the rudiments of the 

 terminal stem plate, a number of columnals, the infrabasals, basals 

 and orals — that the larva emerges as a small barrel or bean-shaped 

 creature with five transverse ciliated bands, an anterior tuft of long 

 cilia, and a deep ventral groove (fig. 56). 



In the best-known species (Antedon adriatica) the length of the 

 free-swimming life varies very greatly, even in difl:erent individuals 

 of the same brood ; some attach themselves after a few hours and 

 immediately proceed to further development, while others are to be 

 found still swimming about after a lapse of as much as four and a 

 half days. As a rule the free-swimming existence terminates after a 

 few hours and is rarely as long as two or three days ; larvae still 

 swimming at the end of that time are abnormal and incapable of 

 fixation. 



After attachment the larva soon assumes the form of a curious 

 little stalked creature composed of a delicate column attached by a 

 spreading base and supporting a calyx consisting of three or five, or 

 often no, infrabasals which are very small, delicate, and difficult of 

 detection, five large united basals forming a cup in which the visceral 

 mass is enclosed, and five equally large orals superposed upon them 



