EXPLANATION OF THE PLATES. 
a. Space between the vitellus and the egg capsule. 
ach. Archenteron. 
acl. Ameboid cells, mesoblastic cells. 
air. Antero-internal calcareous rod. 
al. Anterior lobe. 
alr. Antero-lateral rod. 
am. Ambulacral tube, or member of primitive rosette. 
ap. Anal plate, “centrale.” 
ar. Anterior rod. 
c. Transparent body, in which is contained a branched calcareous rod. 
cap. Capsule. 
ca. Cavity. 
cl. Cell. 
cl pl. Cleavage plane. 
lclpl. First cleavage plane. 
2 cl pl. Second cleavage plane. 
cpl. Central plate, “centrale ” 2 
cr. Calcareous rod. 
d. Polar globule. In PI. I. fig. 2, polar globule 2 
é. Body of young Echinarachnius. 
ed. Edge of the test and junction of the muscular oral structure. 
ifs Muscular filament connecting the wall of the stomach with the epiblast. 
gy: Abnormal segmentation sphere. 
ga. Stomach. 
gm. Mouth of gastrula, blastopore. 
ds Intestine. 
lan. Aristotle’s lantern. 
l. Lateral arm. 
lr. Lateral rod. 
ma. Madreporic opening ; dorsal pore. 
mm. Large segmentation spheres, macromeres. 
0. Thickened floor of a retort-shaped structure. (This is the same as that 
which Metschnikoff calls the invagination of the wall of the pluteus.) 
0e. Oesophagus. 
ol. Oral lobe. 
or. Mouth. 
p- Primitive furrow. In Pl. I. fig. 1, cortical hyaline layer. 
pig. Pigment. 
