404 



INVEETEBEATA 



CHAP. 



developmental facts which have been narrated in this chapter it is 

 obvious that we must commence with the life - history of the 



B 



so.g 



at 



at 



FIG. 321. Median sagittal sections through two fixed and metamorphosing larvae of 



PediceUina echinata. (After Harmer.) 



a.c, iuiiil four; n./i, invaj?inated apical plate; at, atrium ; (if 1 , oral division of atrium; nft, anal 

 division (, i atrium; co, corona ; co 1 , dc^eneratm;; 1 fragments of ciliated cells of corona ; (/n, dorsal or.nan, 

 i.e. fc.rdiral pit; r/i, cpistome ; hep, liver cells; int, iiitc.st.iin 1 ; lr, lateral ridge wliich later, with 

 epistome, divides the atrium into two halves; m, position of the,. mouth; s.o.g, brain J(supra- 

 oesophageal'ganglion ; st, stomach ; ten, rudiments of tentacles of the adult. 



