312 MEAD. 



EXPLANATION OF PLATE XIL 



Amphtirite. 



Fig. 29. From animal (apical) pole : cross, blue ; rosette in middle ; meso- 

 derm cells (red) and somatic-plate cells show through. 



Fig. 30. From animal pole, somewhat later : rosette cells dividing ; (/'-^-^ 

 divided, its lower products indicated by shaded nucleus ; mesoderm and somatic- 

 plate cells as before. 



Fig. 31. Same view : further divisions of cross cells ; rosette left out. 



Fig. 32. Same view : rosette divided ; gl.l. and gl.r., left and right-dorsal 

 mucous glands of umbrella, corresponding to "head-kidneys " in Nereis (Wilson) ; 

 g and g, corresponding cells in ventral arms of cross ; d'^-^-^-^ about to divide (cf. 

 previous Figs. 31, 32); gl.l., gl-r., mucous glands. 



Fig. 33. Same view : further divisions of the cross cells (rosette not figured), 

 J' and ^ dividing ; compare Figs. 31, ^'^ gl.l., gl.r. mucous glands. 



Fig. 34. Same view : dorsal part of umbrella; the lower daughter cells of 

 ^1.2.2.2 (Fig. 22) dividing ; the three products are /', /^ and P ; gl.l., gl.r., 

 mucous glands. 



Fig. 35. From animal pole, somewhat dorsal : ^'-^-^ dividing to form the im- 

 portant landmark (*) ; (/'•^■' divided ; x^ dividing. 



Fig. 36. Nearly same view as Fig. 35, later stage : gl.l., gl-r., mucous glands. 



Fig. 37. Same view, somewhat later, showing left mucous gland cell, gl.l., 

 nearly covered by surrounding cells. 



Fig. 38. Lower hemisphere, about the same stage as Fig. 29 : somatic 

 plate, blue ; mesoderm j7/and M, red; entoderm, stippled. 



Fig. 39. Dorsal view, little later than Fig. 38. 



Fig. 40. Lower (subumbrellar) hemisphere : shows secondary trochoblasts 

 c/c', p^, cp'' ; ap^, ap'', ap'' ; bp^, bp^, bp''. 



