EMBRYOLOGICAL MONOGRAPHS. 
‘ 
. Actinal profile of the anal part of the water-tube (w’) of the Brachiolaria, previous to the appearance of the 
pentagon of lobes. In stage of Pl. VII. fig. 27. 
. Somewhat more advanced actinal profile, showing the ambulacral pentagon, as well as the position of the ten 
limestone rods 7/=r! and 7/!=r!! (the terminal and interradial plates), which are seen through the thickness of 
the larva on the surface of the other water-tube (w). Ina stage intermediate between those of Pl. VII. 
figs. 30 and 31. 
3. A larva in the same stage as the preceding figure, seen from the opposite profile, to show the abactinal area. 
Or 
oo 
K 
10. 
ll. 
13. 
14, 
17. 
18. 
19, 
. The same larva seen from the ventral side of the Brachiolaria, to show the relative position of the pentagons of 
the two areas ; only two of the rods of the abactinal side are seen, while the edges of three of the actinal 
folds (¢) ean be perceived, one above the other, on the footlike projection formed by the folding of the 
water-tube w’. 
. A dorsal view of the Brachiolaria, showing a well-advanced embryo ; the arm-lobes have become indented, the 
arms themselves are separated by a deep cut, the y rods have extended so as to form almost a continuous 
network over the whole abactinal area. The actinal pentagon has assumed the shape of prominent loops 
projecting beyond the footlike oblique fold of the water-tube. 
. The same embryo seen from the actinal profile ; the inner tentacular folds have become tipped with a trian- 
gular point. The thickness of the abactinal surface prevents the network of cells on the edge of the arms 
from being seen. 
. The same, from the ventral side of the Brachiolaria. This figure shows, perhaps better than any other, the 
relative position of the extremity of the two pentagonal warped surfaces. The rough outline of the Starfish 
is due to the manner in which the tubercles of the abactinal surface project above it. The Starfish in this 
condition is at the point of resorbing the larva. The manner in which this resorption takes place is shown 
on fig. 23 of this Plate. 
Quite an advanced embryo Starfish, in which all traces of the appendages of the Brachiolaria have entirely 
disappeared. Each side of the pentagon of suckers is a rosette made up of seven loops ; the limestone par- 
ticles are deposited so as to project at the angle of the arms between the tentacular loops. The mouth is 
movable, the pentagon is not closed, and the Starfish is not yet symmetrical ; the shape of the different 
rays is not identical. 
Magnified view of one of the ambulacral tubes of the preceding figure, with its rudimentary tentacles. 
The young Starfish in which the two pentagons have almost closed, and been brought into parallel planes. 
There has been a great increase in the size of the cut between adjoining rays ; the spines also have grown 
longer and more pointed ; the limestone points of the angle of the the rays have advanced nearer the cen- 
tre. The Starfish is not quite symmetrical, nor are all the arms exactly alike. 
The same young Starfish, from the actinal side, showing the great increase in size of the ambulacral system. 
The tentacles are now long pouches on each side of the main tube. The basal tentacles of one of the arms 
are much farther apart than all the others, and this is the last indication that the ambulacral pentagon is 
not closed. 
2. An abactinal view of one ray, and of the centre of a young Starfish, in which the spines project far beyond 
the edge of the disk. The arm-plates and the interradial plates have become connected by a narrow bridge. 
The original limestone rods are so much thickened by additional deposits that they form elliptical cells, 
which have entirely lost the polygonal character of the younger stages. 
One arm and portion of the centre of the most advanced of the young Starfishes which have been raised from 
the Brachiolariz, from the actinal side. The three pairs of tentacles have suckers ; the deposit of limestone 
of the actinal area has a cellular structure. In this stage the madreporie body is still placed on the lower 
side, on the very edge of the disk. There is a prominent eye-spot at the base of the odd terminal tentacle. 
The young Starfish represented in figs. 13 and 14 is about four months old. 
The same young Starfish as fig. 13, seen from the abactinal side ; the spines are very prominent, long, some- 
what spreading, becoming sometimes even fan-shaped at the extremity. The limestone cells are gradually 
assuming the character of those of the adult, small cells within larger ones; the cut between the rays is 
very deep. 
. The same young Starfish, seen in profile, to show the great development of the abactinal area, and the Echi- 
nus-like arrangement of the spines in the young Starfish. The odd tentacle, with the eye at its base, is 
seen turned up between two of the spines. 
. Two rays and the centre of a young Starfish, about in the stage of fig. 12, seen from the actinal side, in which 
the ambulacral tube is concealed by the limestone deposit ; the pair of terminal tentacles has as yet increased 
but little in size in comparison with the other pairs, which have become so long that they extend beyond the 
edges of the arms. The eye, a brilliant carmine spot, makes its appearance at about this stage. The 
mouth is a well-defined pentagonal opening, limited by the actinal limestone deposit. 
One of the rays and centre of a young Asteracanthion, about one year old, seen from the abactinal side. 
Actinal view of an arm of a young Asteracanthion, probably in its third year. 
20, 21. Magnified views of spines (7), and of rudimentary pedicellarie (p', p"). 
