DIFFERENTIATION IN HYDROID COLONIES. 



145 



thus appear to be unavoidable, do not disturb in any essential 

 respect the conclusions based on the measurements. 



Differentiation within the several hydrocladia will first be 

 considered. 



In Table V., appear the measurements of the length of the 

 mesial nematophore along a line perpendicular to the axis of the 

 internode (upper figures) and the width of the hydrotheca to 

 the tip of the nematophore along the same line (lower figures). 

 The width of the hydrotheca along the line chosen varies, as 

 shown by the table, independently of the length of the nemato- 

 phore along the same line. Neither character is of much value 



Fig. 2 



