74 



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

 and supports the dorsal lobes. The antero-lateral and preoral rods are 



more or less thorny. 



The young sea-urchin carries the typical embryonal spines on the apical 

 plates; they end in four, smooth thorns. The spines of the normal type 

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



Fig. 27. Posterior transverse rod of the larva of Echinometra 

 lucunter; ^'"/x- p. the first rudiment of a pedicellaria. 



Fig. 28. Spines of the young Echinomelra lucunter; the left an 

 embryonal spine, the right a spine of the adult type. 225/^. 



Fig. 28. 



spheeridia are remarkably spinehke. Of pedicellariae only 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.) 



PI. XII, Figs. 2—3. 



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

 in considerable numbers, together with the other pacific species, Echino- 

 metra Mathgei. It was found to have its breeding season at the time of my 

 stay there, in April 1915; fertilization was undertaken on the 6th, and pro- 

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

 4 hours the 16 — 32 cell-stage was reached, and after about 16 hours the 

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

 microscopical examination in these young stages of development. 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 spite 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 



