184 REPORT—1905. - 
connection between the appearance of the proper food in the water and the 
ripening of the adults. In 1898 there was no difticulty in finding ripe 
males and females ; in fact it was their evident abundance which induced 
me to undertake the experiment of rearing the larve on that occasion, as 
the main object of my investigation then was the development of Zchinus 
esculentus. But this year, although hundreds of specimens were exa- 
mined, only two ripe females were found, the second of which, however, 
spawned naturally and provided me with abundance of fertilised eggs. 
These eggs are small and opaque, yellowish-red by reflected light. They 
are about 0-1 mm. in diameter. When sections of the segmentation 
stages are made, it is seen that segmentation leads to the formation of a 
solid morula—not to the formation of a blastosphere as in other Echino- 
derms. At fifteen hours the eggs have become free-swimming larve, 
which‘consist of a superficial sheet of tall ectoderm cells and an interior 
mass of rounded cells. A little later an invagination appears at one end, 
pushing these cells to one side, and in this way the gastrula stage is 
attained. The larva now assumes the shape of a V by the appearance of 
lateral outgrowths, the dorso-lateral arms so characteristically predo- 
minant throughout the later history of the larva. It is then seen that 
the cells which constitute the interior mass of the earliest larva are the 
mesenchyme cells destined to form the supporting rods for these arms, 
and the difference between the development of Ophiothrix and that of 
other Echinodermata is simply due to the precocious appearance of this 
mesenchyme. 
The ccelom is formed, as in Asterids, as a vesicle from the apex of the 
gut and becomes iminediately divided into right and left halves, and the 
left sends out a dorsal outgrowth which forms the primary pore-canal 
and forms the first madreporic pore. Each portion of the celom next 
divides into anterior and posterior halves, and the short pre-oral and 
post-oral ciliated ‘arms’ of the larva are formed. Then when the age, 
nine to ten days, is attained the posterior dorsal arms make their appear- 
ance, completing the equipment of the larva. It is worthy of note that 
the entire larval skeleton consists of two spicules of carbonate of lime— 
a right and a left one. The main branches of the spicules support the 
main dorso-lateral arms ; as new arms are formed branches of the spicule 
extend into them. 
At about eleven days the anterior celom on each side shows a 
posterior swelling, which is at first a solid mass of cells, but soon becomes 
hollow. That on the left side assumes the characteristic five-lobed appear- 
ance which distinguishes it as the hydrocele or rudiment of the water- 
vascular system. That on the right side is at first exactly similar to that 
on the left, and appears at the same time. It becomes hollow, but never 
takes on the five-lobed form ; and later it seems to become again a solid 
mass of cells. There is no doubt at all that it is a rudimentary fellow of 
the hydrocele, and its appearance points to the conclusion that this 
organ was originally double. I have described a right hydrocele 
in the case of Lchinus esculentus and Asterina gibbosa ; but in neither 
case was its nature so beautifully evident as in the case of Ophio- 
thria fragilis. Bury’ maintained that the hydroceele in Ophiuridea 
was formed from the posterior division of the celom. This is a mistake, 
easily expltable if earlier stages are missed out, for the posterior ccelom 
1 « The Metamorphosis of Echinoderms,’ Y.J.4.S., 1895. 
