EXPLANATION OF THE PLATES. 



a. Space between the vitellus and the egg capsule. 



ach. Archenteron. 



a d. Amoeboid cells, mesoblastic cells. 



air. Antero-internal calcareous rod. 



td. Anterior lobe. 



dr. Antero-lateral rod. 



am. Ambulacral tube, or member of primitive rosette. 



op. Anal plate, " centrale." 



or. Anterior rod. 



c. Transparent body, in which is contained a branched calcareous rod. 

 cap. Capsule. 



cav. Cavity. 



d. Cell. 



d pi. Cleavage plane. 



1 d pi. First cleavage plane. 



2 d pi. Second cleavage plane. 



c pi. Central plate, " centrale " ? 



cr. Calcareous rod. 



d. Polar globule. In PI. I. fig. 2, polar globule ? 



e. Body of young Echinarachnius. 



ed. Edge of the test and junction of the muscular oral structure. 



/ Muscular filament connecting the wall of the stomach with the epiblast. 



g. Abnormal segmentation sphere. 



ga. Stomach. 



gm. Mouth of gastrula, blastopore. 



». Intestine. 



Ian. Aristotle's lantern. 



/, Lateral arm. 



Ir. 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.) 



oe. Oesophagus. 



d. Oral lobe. 



or. Mouth. 



p. Primitive furrow. In PI. I. fig. 1, cortical hyaline layer. 



pig. Pigment. 



