434 
H. BUEY. 
liable, render it a far more troublesome object for study than 
the transparent Plutei. 
It is not my intention in the present paper to enter into a 
detailed account of the metamorphosis of the Pluteus into a 
pentagonal Ophiurid, but it will be well to give a few facts in 
support of the statement that the terminals are developed 
round the left enterocoel. In fig. 4 we see that the rapid 
growth of the right and left enterocoels to meet one another 
in the middle dorsal line, has caused the formerly longitudinal 
series of plates to become more or less bowed, and the dorso- 
central to appear distinctly on the dorsal surface of the larva. 
At the same time or rather later, the terminals assume a 
peculiar form (see 18, pi. vi, fig. 11, p 1 — p 3 ), and over each of 
them is developed a marked thickening of the ectoderm. 
Without pausing to describe the next stages we will at once 
pass on to a much later one, represented in fig. 5. The whole 
of the right enterocoel has shifted so far onto the previously 
dorsal face of the larva that the fourth and fifth radials (count- 
ing from before backwards, as in fig. 2) are visible from the 
dorsal side. In correspondence with this the left enterocoel is 
passing round towards the ventral surface, so that the three 
dorsal terminals lie close to the left margin. Besides this 
there has occurred a great shortening of the anterior region 
of the larva, and the most anterior terminal has shifted for- 
wards and across towards the right, so that it now forms the 
anterior median point of the body of the larva (compare 23, 
pi. iii, figs. 1, 3, and 4 f 1 ). The hydrocoel, too, has undergone 
great changes, which cannot be fully described here, but a com- 
parison of figs. 4 and 5 will give some indication of them : 
it will be noticed that in the latter the madreporic plate has 
shifted its position, and lies anteriorly and to the right, hence 
it will be easily understood that that tentacular pouch, which 
formerly (fig. 2) lay just behind the water-tube, now lies at 
the anterior end of the body, immediately under the anterior 
terminal ; while that pouch, which was the most anterior in 
fig. 2, and is on the right in fig. 4, now (fig. 2), lies under 
the second terminal plate, by which its extremity (“ unpaired 
