46 



■was postponed till my return. There, however, it was found that the 

 skeleton had dissolved, except in the very youngest specimens, only one 

 day old, where the skeleton has just appeared in the shape of a pair of 

 three-radiate stars. Although the larvae are otherwise very perfectly 

 preserved there seems to me no reason to give figures of them; they 

 do not present any noteworthy differences from the usual type of larva 

 in regard to the shape of the body. But the information gained about 

 the structure of the body skeleton in the first larval stage is of importance, 

 and I beg to express my gratitude to Dr. Fu jit a for his kind assistance 

 in rearing these larvae. 



Strongylocentrotus pulcherrimus (A. Ag.). 



PI. IX Fig. 5. 

 Th. Mortensen. On the development of some Japanese Echinoderms. p. 544. 



This species being among those which I had, mainly on account of 

 the structure of its pedicellariae and spicules, transferred to another 

 genus (Strongylocentrotus) than that in which it was hitherto placed 

 (Sphaerechinusy) I was very anxious to study its development and ascer- 

 tain whether the structure of its larva was in accordance with that of 

 Strongylocentrotus drebachiensis, — as I expected, — • or not. Already on 

 one of the first days of my stay at the Biological Station, Misaki, I had 

 the pleasure of finding ripe specimens of the species, which is very com- 

 mon there under stones in quite shallow water^). Fertilization was made 

 at once (April 28th) and proved successful. 



The eggs are small yellowish, not very transparent. The cleavage does 

 not offer anything of particular interest. The gastrula stage was reached 

 after about 24 hours, and in the course of the second day the embryos 

 had assumed the shape of small Plutei, rotating in the usual way, i. e. 

 to the right, about their longitudinal axis. 



The young larva agrees in its shape and structure very closely with 

 that of Str. drebachiensis, as described by A. Agassiz*), The posterior 

 part of the body is elongated (PI. IX, Fig. 5), supported by the long body 

 rods. The arms are rather broad and flat, narrowing towards the point. 

 The preoral transverse band is short, rounding upwards at the corners, 

 the frontal area being thus quite narrow. The postoral transverse band 



1) Ingolf-Echinoidea I. 1903, p. 121, 138. 



2) Like so many other littoral Echinoids it has the habit of covering itself with small 

 stones, fragments of plants etc., evidently with the object of disguising itself. 



') A. Agassiz. On the Embryology of Echinoderms. Mem. Amer. Acad. Vol IX 1864 

 Figs. 1 — 18. 



Th. Mortensen. Echinodermenlarven d. Plankton-Expedition p. 90 Taf VII 3—4 

 VIII. 3—5. 



