322 



MEAD. 



EXPLANATION OF PLATE XVIL 



Lepidonotus sp. 



Fig. 8g. Side view, showing that the first furrow sinks in at the animal 

 and vegetative pole at the same time; mem., egg membrane ; solid line i, outline 

 at 11.27 P.M.; 2, outline of furrow at 11.28 ; 3, at 11.29; 4, at 11. 31 p.m.; p.g., 

 polar globules. 



Fig. 90. From animal pole : transition from 4 to 8-cell stage ; cross-furrows 

 at right angles to each other. 



Fig. 91. From animal pole : 8-cell stage from life. 



Fig. 92. Side view: 16 to 32-cell stage (cf. Amphitrite, Figs. 12 and 21, Pis. 

 X, XI). 



Fig. 93. From animal pole : thirty-two to sixty-four cells (cf. Amphitrite, Fig. 

 17) ; pg., polar globules inside the apical cells. 



Fig. 94. Lower (vegetative) hemisphere of same egg. 



Fig. 95. Similar stage from vegetative pole : transparent ; the cross and 

 rosette cells (animal pole) in dotted lines. 



Fig. 96. Similar stage from side, showing segmentation cavity. 



Fig. 97. Side view, later : trochophore begins to swim ; shaded cells are pro- 

 totrochal (cf. Figs. 27, 28, Amphitrite, 77 and So, Clymenella). 



Fig. 98. Actual section of stage like Fig. 96 shows polar globules inside 

 of apical cells, p.g. ; segmentation cavity, seg.cav. 



Fig. 99. Same egg as Fig. 96, from animal pole. Arrow indicates direction in 

 which the trochophore rotates. 



Fig. 100. Later stage : cross shaded, two cells in each arm (cf. Fig. 29) ; 

 p.g, one polar globule, — the other within segmentation cavity. 



Fig. ioi. From animal pole: rosette and part of cross ; three cells in some of 

 the arms of cross, probably in all ; gl., cell corresponding to mucous gland in 

 Amphitrite (cf. Fig. 32). 



Fig. 102. Optical vertical section : the nuclei of the eight elongated vegetative 

 cells are migrating inward. The cells 4, 4, are a'', b'', c^, or d^. 



Fig. 103. Actual section, vertical, somewhat later. 



Fig. 104. Optical section, gastrula : p.g., polar globule ; prot., prototroch ; 

 mes., mesoderm cell probably ; bp., blastopore. 



