3l6 MEAD. 



EXPLANATION OF PLATE XIV. 



Amphitrite. 



Prototroch and paratroch brown ; somatic plate, blue ; mesoderm, red ; ento- 

 derm, stippled. 



Fig. 53. Lower hemisphere, dorsal : par.v.lft., left-ventral paratrochal cell ; 

 par.v.rt., right-ventral paratrochal cell ; the two cells between them give rise 

 after one division (cf. next figure) to the dorsal paratrochal cells. 



Fig. 54. Same view : last division of paratrochal cells ; par.d.lft., leit-dorsal 

 paratrochal cell ; par.v.lft. and par.v.rt., left and right-ventral paratrochal cells. 



Fig. 55. Same view, later: paratroch completely differentiated; par.d.rt, 

 right-dorsal paratrochal cell ; others as in Fig. 54. 



Fig. 56. Lower hemisphere : beginning of concrescence of somatic-plate 

 cells from either side ventral to the paratroch ; proc, area of future proctodseum. 



Fig. 57. Same view, later: further concrescence of somatic plate: letters 

 x^, d^-^, etc., indicate from what cells the respective areas are derived. 



Fig. 58. Dorsal view of stage like Fig. 56 : interruption of prototroch ; cells 

 with shaded nuclei ; i", i*, I^ etc., descended from d'^-^-' (cf. Fig. 30). 



Fig. 59. Dorsal view : gl. and gl., dorsal umbrellar mucous glands (cf. 

 Figs. 32, 33, etc.) ; mesoderm bands, mes., composed of six cells each ; interruption 

 in prototroch nearly completed ; other letters as before. 



Fig. 60. Dorsal view : prototroch interruption obliterated by concrescence of 

 prototroch cells. 



Fig. 61. Right side : surface view of prototroch; the rest in optical section, 

 showing entoderm cells, eni., somatic plate, som.pl. ; mesoderm band — three cells, 

 teloblast dividing, mes. ; paratroch cells, par.d.rt., par.v.rt., etc. 



Fig. 62. Left side : same egg as Fig. 59 ; entoderm and mesoderm bands 

 in the interior; letters as before. 



Fig. 63. Right side, later larva, showing prototroch, paratroch, stomodasum 

 (stomod.), etc. 



Fig. 64. Optical section from left side : prob., problematic bodies ; gl-l-, 

 left-dorsal umbrellar mucous gland (cf. Figs. 30 and 59) ; gl., ventral umbrellar 

 mucous glands ; duct, duct of gland ; ext.op., opening of duct to exterior ; vac, 

 vacuoles in cells of prototroch ; stomod., stomodseum ; muc, mucous glands 

 of subumbrella ; n, groove separating head segment from first trunk segment ; 

 par.v.lft. and par.d.lft., ventral and dorsal paratroch cells of the left side ; proc, 

 proctodaeum. For later stages see text Figs. XI-XVIII. 



