Ill 



the locality where the adult specimens were found, the sand being, of 

 course, first examined microscopically in order to ascertain that no young 

 specimens from outside wore contained in it. This proved to give an ex- 

 cellent result ; the young sea-urchins now did not die, but lived and thrived 

 well. On leaving Japan I carried a culture of the young Peronellas along 

 with me to Australia; they stood the transport very well. On my arrival 

 in Sydney the jar in which they were kept happened to be turned over, 

 and I had to fill it up with water from Sydney Harbour. They stood that 

 very well too. It was not until the 29th of October that the last specimens 

 were preserved. Most of them had died already by that time - - but a 

 few were still in good condition, having reached a length of the test of 

 0.6 mm, while the newly metamorphosed urchin is only 0.2 mm long. The 

 growth is not very considerable, it is true; but this is due, I do not doubt, 

 to the lack of sufficient food supply. It seems beyond doubt that under 

 good conditions it will prove very well possible to rear this sea-urchin to 

 a much larger size, if not to full size - - an experiment which would be 

 of very considerable interest. - The rate of growth of this species under 

 natural conditions most probably will be considerably faster. I regret 

 being unable to give information about this matter in the same way as 

 I did it for Erhinarachnius e.irentricus, having found no young specimens 

 in I he place where the adult specimens were collected. 



The eggs are ca. 0.3 0.4 mm in diameter, yolk-laden and opaque. They 

 are surrounded by a thick mucilaginous coat, without pigment. The cleav- 

 age is total and regular. At the age of ca. 5 hours the embryo has reached 

 the blastula-stage; it is much folded (PI. XV, Fig. 1), the folds often being 

 arranged in four meridians so that the embryo has the appearance of 

 being in the four-cell stage. The folds then gradually disappear, the egg- 

 membrane widening contemporaneously so as to give room for the now 

 somewhat larger embryo. At the age of 8 hours the embryo has developed 

 cilia and begins to rotate within the egg membrane, and at the age of 

 about 10 hours it breaks through the membrane and is liberated; it has 

 now the shape of a somewhat elongate gastrula. 



Regarding the entoderm formation it is stated in the preliminary notice 

 that it takes place "not as a real invagination, but more as a strong growth 

 of cells at the oral end, and there is no gastrula mouth". The study of 

 sections of the embryos has shown this statement to be wrong. At the 

 age of 8 9 hours a rapid growth of mesenchyme cells from the truncated 

 oral end of the embryo takes place (PI. XV, Fig. 5), which may proceed 

 so far as to fill out the blastocoel cavity almost completely. At the age 

 of ca. 12 hours, sometimes earlier, the gastrula invagination begins (PI. XV, 

 Fig. 6), in the usual way. 



