478 WILSON. 



PLATE XIX. 



[All of the figures from preparations.] 



Fig. 71, Longitudinal optical section about the time the blastopore closes. Posi- 

 tion of the prototroch indicated by the faint lines (9 h. 45 m.). 



Fig. 72. Similar view after the first gemmation of the primary mesoblasts (the 

 same specimen shown in Fig. 41) (7 h. 30 m.). 



Fig. 73. Slightly later stage, showing gemmation of one of the mesoblasts. The 

 section is somewhat oblique and shows the hinder part of the other mesoblast wedged 

 in between the dividing cell and the posterior teloblast (8 h. 30 m.). 



Fig. 74. Right view of the same specimen shown in Fig. 57. Nephroblast pass- 

 ing beneath the prototroch. Derivatives of c^ in division (9 h. 30 m.). 



Fig. 75. Later stage in similar view. Head-kidney extending itself beneath the 

 post-trochal cells (offspring of <:'-) (12 h. 30 m.). 



Fig. 76. Similar view of the same embryo shown in Fig. 66. Extension and canal- 

 ization of the head-kidney (11 h. 30 m.). 



Fig. 77. Left side-view of about the same stage shown in Fig. 67. The head- 

 kidneys nearly surround the body, the prototroch is double; prostomial depression 

 still present; first appearance of the pigment (14 h.). 



Fig. 78. Left side-view of same stage as Fig. 68. Prototrochal region in surface- 

 view (also the left residual teloblast), the remainder in optical section (^cf. Fig. 88). 

 Formation of the pigment-area; its relations to the stomatoblasts (13 h. 30 m.). 



Fig. 79. Ventral view of the same stage. The position of the residual teloblasts 

 indicated in optical section (15 h. 45 m.). 



Fig. 80. Similar view of later stage. Stomod^al arc, pigment-area, mesoblast- 

 bands (18 h.). 



Fig. 81. Completion of the stomodaeum, demarcation of the pigment-plug, posi- 

 tion of the mesoblast-bands. Last traces of the residual teloblasts (?) (20 h.). 



Fig. 82. Left side-view of the same specimen. Prototroch, eye-spot, and frontal 

 bodies in surface-view. The stomodaeum and pigment-area in juxtaposition (20 h.). 



