68 THE APODOTJS HOLOTHUEIANS 



pear to be the most restricted in their movements; for while both the sub- 

 terranean and the free-living forms are more or less continually moving about 

 in search of food, they seem to remain for long periods of time in a single 

 spot. As a rule, Syuaptids do not thrive in aquaria, but some of the sub- 

 terranean forms will do very well if there is an abundance of pure sea- 

 water. The free-living forms are very sensitive to changed conditions and 

 soon die in ordinary aquaria. The length of life and the rate of growth are 

 wholly unknown, though there is reason to believe that both are closely cor- 

 related with the abundance of the food supply. It is hard to say whether 

 Synaptids have any enemies of importance or not ; so far as we know, they are 

 not sought after by any animals, but it is difficult to see why they, would not 

 serve, as well as worms, for food for fishes. Some starfishes and a few mol- 

 lusks are known to eat holothurians and some Synaptids may be destroyed by 

 such foes. Parasites are quite common; some half dozen sporozoans, a sponge, 

 several trematode worms, a rotifer, a crustacean, and half a dozen mollusks 

 are already known, which live upon or within some Synaptid, and there are 

 doubtless others which have not yet been noted. Some of these probably 

 obtain little, if any, nourishment from their host, but some of the internal 

 forms are true parasites of the most degenerate kind. Whether any of them 

 seriously enfeeble their host is, however, an open question. 



Abnormal individuals (aside from some diversity in the .number of tenta- 

 cles) have only been reported in the case of Synaptula hydriformis, where the 

 young are sometimes more or less grown together in pairs (Plate VI, fig. 22) 

 or triplets, occasionally even in quartets and quintets. It is more than doubtful 

 whether these monstrosities ever reach maturity, but one adult with only 3 

 radii and 11 tentacles has been recorded. Additional tentacles and abnoi'mal 

 calcareous particles are frequent and are known in many species. So far as 

 the human race is concerned, the Synaptidne are absolutely useless ; none of 

 them serves as food or even as the source of articles or substances which are 

 of the least value to man, nor do they furnish food for any animal of commer- 

 cial importance. The geological history of the Synaptidae is very imperfectly 

 known, but calcareous particles clearly referable to members of the family have 

 been found in Eocene rocks, and there is reason to believe that the family 

 dates back to the Cretaceous period at least. 



TAXOLOGY. 



The classification adopted in this report has already been discussed and 

 fully outlined (pp. 14-17), but a few words may be added here in explana- 

 tion of the principles which have been used in determining the validity of the 

 genera and species herein accepted. In attempting to distinguish a "good 

 species," it is essential that the possibilities of individual diversity should 



