DIFFERENTIATION IN HYDROID COLONIES. 



149 



hydrocladium (owing to a slight rotation out of the plane of 

 the other hydrothecse). Nothing sufficiently definite can be said 

 about the length or thickness of the hydrothecse. There is a 

 perceptible increase in size of the hydrothecae in Hcl. 21, toward 

 the tip. It is much less in the other hydrocladium ; and meas- 



Hcl 10 Hd 21 



Fig. 3. A. inconspicua, X 45- 



urements of others show that it is not characteristic and typical, 

 for either dimension. 



A. lophocarpa. — The few colonies of this species at hand are 

 all imperfect, both as to stems and hydrocladia. HoA-ever, the 

 hydrocladia taper from base to tip, the first hydrotheca on each 



