EMBRYOaENY 



207 



suckers. They were formerly considered as worms 

 or articulate animals, until their embryogeny became 

 known. ' They possess an amorphous body in which 

 often nothing of limb formation remains and only a 

 trace of extremities can be found/ l Some characters, 



FIG: 41. Sacculini carcini, fixed onCarcinus 

 mcenas, whose abdomen is exposed. a, 

 eye ; b, antennae ; c, anus of crab ; d, shell 

 opening ; e, stalk ; f , root of web, envelop- 

 ing the intestines of the host, leaving 

 the germinal region free. 



(After Hertwig : ' Zoologie.') 



which remind one of free-living Swimming Crabs (two 

 suspended egg sacs), furthermore a series of transitional 

 forms between Swimming Crabs and these amorphous 

 beings, and above all their evolutionary history (em- 

 bryogeny) these were the factors which cleared up 

 their systematic position. They pass through the 

 typical Cyclops stage of the Copepods, and only when 



1 R. Hertwig : Lehrbuch, p. 382. 



