34. 
35. 
36. 
EMBRYOLOGICAL MONOGRAPHS. 
. Gastrula three days old. The diverticulum of the gastrula cavity begins to be formed on the left and right 
sides. « shows the left diverticulum. 
. Longitudinal section of a gastrula soon after its escape from the egg ; the left and right enteroccelum pouches 
are indicated. 
The same stage as fig. 20, seen from the left side : Z m, the invagination of the ectoderm which eventually 
forms the larval mouth. 
2. The same stage as fig. 20, seen from the right side. 
. Embryo at the beginning of the fifth day, seen from the left. @, point of separation of the gastrula cavity and 
the enterocceluin ; b indicates the position of the gastrula mouth, Gm, which has now disappeared. 
. Transverse section of an embryo in the stage of fig. 23. 
. Longitudinal section of an embryo at the end of the fourth day ; in which the gastrula cavity a is still in 
communication with the enteroccelum. 
. Longitudinal section of an embryo at the end of the fifth day; the communication between the gastrula cavity 
and the enteroccelum has become completely shut off at a. 
. Larva of the seventh day, seen from the left side ; the intestine, of which the position is merely indicated, has 
been removed, to show the mesentery, 1, placed behind it. The arrow indicates the communication be- 
tween the enteroccelum of the larval organ and the enteroccelum surrounding the intestine. 
. Larva in the same stage as fig. 27, from the anterior side : the position of the intestine is only indicated. 
30, 31. Different views of a larva on the sixth day. 
. Seen from the left side: a, the larval organ (the brachiolarian appendages) ; 6, its anterior, c, its posterior 
lobe ; d, the button-like projection on the creeping surface of the larval organ. 
. The same as fig. 29, seen from the anterior and left side. 
. The same, seen facing the creeping surface of the larval organ. ; 
2. Larva of the sixth day, seen from the left. The hydroccelum has become five-lobed, 1, 2, 3, 4, 5, its five lobes ; 
the position of the mesentery on the other side of the digestive cavity is indicated as if seen through it. 
The arrows indicate the communication between the larval enteroccelum, the hydroccelum, and the entero- 
ccelum surrounding the digestive cavity. 
. Larva of the seventh day. The hydroceelum is apparently shut off at @ from the larval organ ; communica- 
tion between it and the larval organ, however, is still clearly to be made ont, and is indicated by the 
arrow ; b, formation of an ambulacral lobe (1) in the mesoderm below the hydroccelum ; c, a band of con- 
nective tissue, not always found in this position. 
Larva of the seventh day, from the posterior side. JZ s, the larval esophagus ; S's, pouch of the digestive 
cavity extending towards the hydroccelum, which later trends towards the cesophagus of the young Starfish. 
The madreporic canal is abnormally early developed. 
Exterior view of the same larva, showing on an upper plane the dorsocentral plate, C, with interradials 
JR, TRy JR3, Thy, JR, and one of the terminal plates, 73 ; on the next somewhat lower plane are the 
terminal plates 7, 73, 7’, and on a still lower plane, 7). 
Longitudinal section through the same larva, seen from the anterior side ; @ shows the broad open communi- 
cation between the enteroccelum of the larval organ and the hydroccelum, as well as the communication 
between the dorsal pore and the enteroccelum of the larval organ. 
. View of a whole embryo, seen from the right and lower side. 
. View of a larva partly cut open, seen from the right side. B/!’, central blood system. @, mesoderm plate 
covered by the entoderm of the enteroccelum ; this has taken the place of the larval cesophagus, which has 
now disappeared. 
. A larva of the eighth day, seen from the left side. 
. A similar larva, creeping. @ and } in both these figures denote the anterior and posterior larval lobes. 
. The surface of the larval organ of an embryo somewhat more advanced than figs. 39, 40. 
. Larva in about the same stage as fig. 41, seen from the right side. 
. Larva on the eighth day, seen from the right side, showing the position of the blood cavity, B7, in the mesen- 
tery adjoining the fifth interradial, JR, in the position where the madreporic plate will eventually be 
formed. 
. Larva at the beginning of the ninth day, seen from the left. 
. Larva at the end of the eighth day, seen from the anterior side. 
. Larva of the ninth day, cut open close to the surface on the left, to show the shape of the hydroccelum lobes, 
their unequal development, and the formation of the first and second ambulacral plates. 
. Larva of the tenth day, seen from the anterior side. 
. The same, from the anterior and left side. 
. Larva of the tenth day. This larva still retains a large larval organ : seen from the left, the section is so 
made as to show the relation of the five lobes of the ambulacral and antiambulacral areas. 
