71 



and two short lateral processes, the lower of which is backwards directed 

 and supports the dorsal lobes. The anlero-lateral and prcoral rods are 

 more or less thorny. 



The young sea-urchin carries Ihe typical embryonal spines on tlie apical 

 plates; they end in toui, smooth thorns. The spines of the normal tyj)e 

 aie characteristic in having a very long central thorn (Fig. 28). The 



)\ 



KiR. 27. Posterior I rMiisvcrsi' rod of tlu' l;n\;i of Echindmcira 

 lucunler; ^"°/,. p. Uic lirst nidimcnt ol ;i pciliccllarin. 



Fig. 28. Spines of liie young Hrhinonu'tra liiiuntfr; Uie iefl an 

 emliryonal spine, tlie riglit a spine of tlie adult type, -^/i- 



Fia. 28. 



sphirridia are remarkably spinelike. Of pedicellaria? oidy the ophicephal- 

 ous form has appeared even in the oldest of the specimens. For the rest 

 I cannot enter on the study of the postlarval development on this occasion. 



Echinometra oblonga (Blv.) 



Fl. XII, Figs. 2—3. 



In the rock ponds at the coast of Hawaii, near Ililo, this species occurs 

 in coiisideial)le numbers, together with the other pacific species, Erhino- 

 melrn Malluvi. It was found to have its breeding season at the time of my 

 stay there, in April 1^15; fertilization was undertaken on the 6th, and pro- 

 ved to be successful. Tlie eggs are very small, opaque. In the course of 

 4 hours the IG — 32 cell-stage was reached, and after about l(i hours the 

 gastrula stage. On account of its opaqueness it forms a poor object for 

 microscopical examination in these young stages of develoi)ment. On the 

 second day the embryos had assumed the Pluteus shape; for a few days 

 more the larvae were thriving well, but then the culture degenerated, 

 doubtless because the water was not very good. In sjjite of repeated 

 attempts I did not succeed in getting another culture, so that information 

 can be given only of the first larval stage. 



The shape of the larva (PI. XII. Figs. 2 — 3) is somewhat unusual, the 

 upper edge of the anal lobe projecting almost at a right angle from the 

 body, like a lip. The postoral band does not follow the edge of the anal 

 lobe, or rather it has the appearance that it does not do so, the part inside 



