408 Mr. J. S. Gardiner on the Distribution 



that tliey belong to adults living in the deep sea, Mortensen's 

 conclusion would point to there being a bank in the Sargasso 

 Sea or to the adults living in the floating weed. So certain, 

 too, are the students of the Enteropneusta of the limited 

 distribution of their larvas that, if there is one species of that 

 group in a locality, they unhesitatingly refer to it any 

 Tornaria that may be found in the same locality, even a 

 single specimen, and describe it as its larva. 



At the present day the keeping and rearing for experi- 

 mental purposes of Echinoderm larvae is a regular business 

 and one of which I had some experience in 1895-96. Now 

 those larvffi wliich iiave been worked at do not feed for 3 to 

 4 days after they have definitely assumed the larval con- 

 dition, and they finally metamorphose after 20 to 40 days*. 

 Any deduction from these facts must be in absolute disagree- 

 ment with Mortensen^s results ; but possibly in the sea the 

 period of Echinoderm larva? before metamorphosing is quicker. 

 However, one must conclude that they may at times be drifted 

 for 20, 40, or some even 60 days at tlie mercy of the currents. 

 Nevertheless I only found in the localities cited above larvce of 

 Echinoderms off Eotuma, 4 plutei, 1 bipinnaria, and 1 bra- 

 chiolaria, each from a different sample of plankton. I may 

 parenthetically remark that my observations at Naples 

 showed that the more food given to these and all larvae the 

 quicker they grow and metamorphose, other conditions being 

 the same. All the Echinoderm larvae float in the tanks near 

 the surface of the water so long as they are healthy and the 

 water be undisturbed, while the typical trochosplieres sink 

 down to varying depths, some of the largest and really 

 healthiest ones almost lying on the bottom both by night 

 and day. To summarize and to conclude, it would appear to 

 me that no results in distribution can be expected, so far as 

 the Indo-Pacific is concerned, from Echinoderms — and 

 probably also from Enteropneusts — other than the Crinoids, 

 the motile condition of the larva? of which would seem to be 

 scarcely longer than that of the planulaj to be mentioned 

 later. 



The typical trochosplieres, both Molluscan and Annelid, 

 are more difficult to keep in tanks than tlie Echinoderm larvee. 



* Mr. L. Doncaster has given me tlie following data : — 



Fertilized. Metamorphosed. 



34 days. Strongylocentrotus d X $ May 14. June 17. 



82 „ Echinus JX$ June 23. July 25. 



38 „ Echinus 5 X Strongylocoitrotus S • March 5. April 12. 



27 „ „ „ May 16. June 11. 



27 ,, „ ,, June 14. July 11. 



