2 20 CONK LIN. 



EXPLANATION OF PLATE VI. 



Fig. 6i. A stage after the formation of 5A, 56, and 5C, but before the forma- 

 tion of sD, showing the ectoblast in position. Mesoblastic bands hard to dis- 

 tinguish and not shown. 



Fig. 62. Anterior view of egg of about same stage as Fig. 61. The apical 

 cells, rosette series, and turret cells are shown. In this and the following figure 

 the cells 2b'-=-^-'-' (V) and 2b'-^-=-'-^ (V) should probably be designated ib'-^-^-'-^ 

 and ib'-=-^-^-^ while the first velar row is probably formed, just ventral to these 

 cells. (See Note, p. 204.) 



Fig. 63. Narrowing of the blastopore. 



Fig. 64. Dorsal view, showing apical cells, rosette series, posterior turrets, and 

 proximal cells of posterior arm. The apex is far in front of the polar furrow. 



Fig. 65. Closing of the blastopore and beginning of the stomodaeum. The 

 apex has moved forward until it can be seen from the ventral side ; it lies to the 

 right (left in figure) of the mid line. Between the apex and the first velar row are 

 the seven large cells of the apical cell plate. Both first and second velar cell rows 

 are indicated. Many rows of cells radiate from the anal cells, running forward 

 over the ventral surface posterior to the blastopore. The enteroblasts are turned 

 to the right (left in figure) by the laeotropic torsion of the posterior region. In 

 Figs. 65-73 the cells labelled ib'-^-^-"-' and ib'-^'^-^-^-^ should probably be ib'-^-'-^-^-' 

 and ib'-^-^-^-^-^ respectively, and the arrows showing the derivation of these cells 

 should be moved one cell nearer the apex so as to connect ib'-^-'-^-^ and ib'-^-^-^-^-'. 



Fig. 66. Stage similar to the preceding, showing still more clearly the apical 

 cell plate and the first and second velar rows. 



Fig. 67. Apical view of same, showing apical cells, rosette series, posterior 

 cell plate, apical cell plate, and first and second velar rows. 



Fig. 68. Stage similar to the preceding, but showing in addition the stomo- 

 daeum, the shape and extent of the mesenteron, the division of the cell 5D and 

 its rotation over to the ventral side, and the consequent looping of the intestine 

 to the right (left in figure). 



Fig. 69. Egg of C. plana, showing some of the cells of the apical cell plate and 

 of the first and second velar rows. In Figs. 69-71 the cell marked 2b'-'-' is prob- 

 ably ib'-=-=-=-=-'-= whereas the median cells of the first velar row (V) probably 

 represent the derivatives of the anterior tip cells (2b''). 



Fig. 70. Egg of C. plana, showing further stages in the degeneration of the 

 cells marked 2b''''' (?). 



Fig. 71. Egg of C. plana, showing the earliest stage observed in the degenera- 

 tion of the cells marked 2b'-'-' and 2b'-'-^. 



Fig. 72. Egg of C. plana, showing apical plate and velar cell rows. 



Fig. 73. Egg of C. plana a little older than the preceding, showing apical 

 plate, velar rows, mesoblast, and enteroblasts. 



