251 



einm 



enpv 

 (c) 



ewil 



(d) eml 

 id) 



entnt 



Fig. ?,. A. Optical section at the sixme plane as Fig. 2, B, but of a slightly older 

 stage showing the teloblast-like budding of the right {emn) and left (emr) ectomeso blast 

 and also the migration of the median {emm) ectomesoblast. The J/'s have each budded 

 off a small entomesol)last cell (e). B. Optical section from dorsal side and at right angles 

 to the prototroch. The J/'s liave begun to migrate laterally leaving behind the small 

 entomesoblast cells (e, e). I, lateral ectomesoblast cells from right and left intergirdle 

 regions of the first quartet; re, rudimentary cells sunk into the cntoblast cells and de- 

 generating. In this and the following sections the prototrochal cells (p) are reeled in 

 diagonal lines. C. Optical section from the left side. The blastopore (bl) has migrated 

 toward the prototroch. An ectomesoblast cell from the first quartet (a) in sinking, pro- 

 bably from the b ann of the cross. D. Optical section from the ventral side of a con- 

 siderably older stage. There are three cells in each mesoblast band and the small ento- 

 mesoblast cells derived from the vl/'s are shown at the posterior end of the enteron. 

 The ectomesoblast is, in part, ])ecoming transformed into larval muscles. 



