AN INTRODUCTION TO THE METAZOA 



G. A complex Metazoon (Lumbricus). 



z g.c. pb.e 



CELL DIVISION 

 (Embryological 

 development) 

 Zygote (2) pro- 

 duces body 

 containing 

 germ cells (g.c.) 

 and three layers 

 of specialized 

 somatic cells, 

 the ectoderm 

 (ec.), mesoderm 



(ws.), and 

 entoderm (en.). 



CELL DIVISION 

 (Gamete for- 

 mation) 

 Certain germ 

 cells produce 

 one egg (<) and 



two polar 



bodies (pb.); 



others produce 



many sperms 



PERMANENT 

 CONJUGATION 

 (Fertilization) 

 One sperm 

 unites with 

 one egg form- 

 ing a zygote 



CELL DIVISION 

 ( Embryological 

 development) 

 Zygote (2) pro- 

 duces body, etc. 



