3IO MEAD. 



EXPLANATION OF PLATE XL 

 Atnphitrite. 



Cross and somatic plate, blue ; prototroch, brown ; mesoderm, red ; entoderm, 

 stippled. 



Fig. 17. From animal pole : the spindles In the four apical cells indicate 

 the divisions resulting in the rosette ; end view of spindles in the primary trocho- 

 blasts of second generation (colored brown). 



Fig. 18. From animal pole : the primary trochoblasts of third generation, i.e., 

 the cells of the primary prototroch (brown), have developed cUia ; apical rosette, 

 fli.j-i/i.j ; parent cells of cross in blue ; trochophore now rotates in direction in- 

 dicated by arrow, ar. 



Fig. 19. From vegetative pole, about same age as Fig. 18 : primary meso- 

 blast cell M, or d'^, being formed (colored red) j somatic-plate cells in blue ; 

 primary prototroch in brown as before. 



Fig. 20. Same view : mesoderm cell fully formed ; superficial position of D. 

 The two figures show an unusual time variation, the division producing d'' (= M) 

 being tardy in Fig. 19 ; other cells colored as before. 



Fig. 21. Same egg as Fig. 20 from right side: color as in previous figures; 

 cross and somatic plate, blue, etc. 



Fig. 22. Same egg from left side. 



Fig. 23. From vegetative pole, somewhat later : entoderm plate stippled ; only 

 posterior prototrochal cells visible ; cUiated. 



Fig. 24. LUce Fig. 18, somewhat later stage. 



Fig. 25. Frorn left and below : same egg as Fig. 23. 



Fig. 26. Froiri right side and below : same egg as Figs. 23 and 25. 



Fig. 27. From left side, about same stage as last figure : shows ciliation of 

 ap^ {= «■•'•'•'), which in Nereis is non-ciliated (Wilson). 



Fig. 28. Same egg as Fig. 27 from ventral side. 



