4fi 



was postpoiUMl lill my itiuiii. Tlicre. however, it was found Ihat the 

 skeleton luul dissolvod. except in the very youngest specimens, only one 

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

 Ihree-radiate stars. Although the lai\a' art' olherwise very perfectly 

 preserved Iheie seems lo me no ii'ason lo tjive (igures of Ihem: lliey 

 do not present any noteworliiy dilTerences from the usual type of larva 

 in regard lo the shape of the body. Hut the information gained about 

 the structure of the body skeleton in the first larval stage is of imi)ortance, 

 and I beg to express my gratitude to Dr. Fujita for his kind assistance 

 in rearing these larvae. 



Strongylocentrotus pulcherrimus (A. Ag.). 



I'l. I.\ Fig. o. 

 I'll. Morli'iiMMi. On 11k' <k'\i'l()|)riu'iil ol soiiii' .lapaiu'sc Echinoderms. p. .")ll. 



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

 the structure of its pedicellariae and spicules, transferred to another 

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

 (Spha'reihiniis)^) I was very anxious to study its develo])menl and ascer- 

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

 SlroiuiiilorciUrolus drohachiensis, — as 1 expected, — or not. Already on 

 one of the first days of my stay at the Biological Station, Misaki, 1 had 

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

 mon there under stones in (juite shallow water-). Fertilization was made 

 at once (April 2(Sth) and proved successful. 



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

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

 after about 21 iiours, and in the course of the second day the embryos 

 had a.ssumed 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 .S7/'. drobachicnsis, 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 (|uite narrow. The ]iosloral transverse band 



') IiiRolf-Echinoidca I. l'.Mi:i, p. 121, l.i.S, 



■-) Like so many other litloral lu'lilnoids it has liu' hahil of covering ilsell with small 

 stones, fragments of plants etc., evidently witli the ohjcct of disguising itself. 



^) A. Agassi/,. On the Embryology of Echinoderms. .Mem. Amer. Acad. Vol. l.\. 186-1. 

 Figs. 1—18. 



'I'll. .Morteiisen. Echinodermeiilarveii d. Planktoii-Expedilion p. 9(1. Taf. \\\. .'i — I. 

 \ 111. :! .'). 



