DIFFERENTIATION IN HYDROID COLONIES. 



151 



of the hydrotheca along the same Hne from the base of the 

 nematophore (see Fig. 4, BHcl, hth.12). 



■^iK r~> 



Hell// 



Fig. 4. A. struthionides, X 45- 



Neither this nor the following species lends itself easily 

 to a determination of colonial differentiation, as does A. pluma. 

 Both are variable, often luxuriant growers. Colonies of A. 



