CELL-LIXEAGE. 



19 



7) and slightly anterior to the latter. Sections show that these 

 cells are budding forth smaller cells into the cleavage-cavity. I 

 am nearly certain that these cells are not derived from the ento- 

 blast ; and their position is such that an origin from the primary 

 mesoblasts is improbable. They are often closely wedged in 

 between the overlying ectoblast-cells, and all the appearances 

 indicate that they have been derived from the latter. From 

 their position I believe it probable that these cells have been de- 

 rived from the two lateral cells of either the third or the second 



Fig. 7, Aricia. Frontal optical section^ of early embryo of Aricia, showing the 

 parallel mesoblast-bands (;//, ;;/) extending upwards frona the primary mesoblasts, 

 M, M, behind the entoblast plate (cf. Figs, i, C and 2, A, which show the 

 same individual in different positions). At the sides of, and slightly anterior to, 

 the mesoblast-bands are the two mesoblast-cells {y, y) of probable ectoblastic 

 origin. 



quartet — /. c, from derivation of r^ and d^, or of r" and a'^ {Cf. 

 Fig. 2, A) — and that they accordingly are comparable to the 

 ** larval mesenchyme" or *' secondary mesoblast" (/. r., the ecto- 

 mesoblast) of Unio and Crepidiila. Future investigation must 

 determine whether this surmise be correct, and what is the ulti- 

 mate fate of these cells, but the facts give, I think, good reason 



1 Confirmed by actual sections. 



