404 



INYERTEBEATA 



CHAP. 



developmental facts which have heen narrated in this chapter it is 

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



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

 Pedicellina echinata. (After Harmer.) 

 a.e, anal cone ; ap, invaginated apical plate ; at, atrium ; ail, oral division of atrium ; a(2, anal 

 division of atrium ; co, corona ; co^, degenerating fragments of ciliated cells of corona ; do, dorsal organ, 

 i.e. cerebral pit ; ep, epistome ; Tie'p, liver cells ; iiU, intestine ; It, lateral ridge which later, with 

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

 oesophagearganglion ; s(, stomach ; ten, rudiments of tentacles of the adult. 



