IV. i INITIAL STRUCTURE OF THE GERM 



221 



The cells of the third and fourth quartettes do not develop 

 at all. 



A ^ macromere (1 A 1 D), however, segments partially, to 

 form a mieromere of the second quartette, from which secondary 



9 



FIG. 130. Patella. Development of isolated cells of first quartette 

 and of the whole quartette, a, Isolated I 1 ; 6, its first division ; c, its 

 second division ; d, after 12 hours ; e, after 22 hours, showing apical cells 

 and secondary trochoblasts ; /, first division of isolated first quartette ; 

 g, second division. (After Wilson.) 



FIG. 131.- Patella. Isolated cells of second quartette, a-c, Cleavage; 

 d. after 24 hours, showing secondary trochoblasts and ? preanal cells. 

 (After Wilson.) 



trochoblasts are later developed, and one of the third. Subsequently 

 an archenteron is invaginated (Fig. 132). So the -^ macromere 

 (2 A 2 D) forms a mieromere (3 a 3 d} and gives rise to a 

 larva with entomesoblast (D) or entoblast only (A C). 



