EXPLANATION OF PLATE XVL 



Fig. 



1-3. Rhipidodendron splendidum, St. (Stein), vol. i. p. 285. — Flabelliform com- 

 pound colony-stock or zootheciuni, consisting of several hundred closely- 

 united tubules, the entire structure representing the product by repeated 

 subdivision and excretion of a primarily single monadiform animalcule, X 400 ; 

 2, young zootheciuni, constructed up to the point of bifurcation by a single 

 monad, which then dividing by longitudinal fission, has produced two 

 parallel tubes, x 600; 3, an isolated monad, x 11 50. 



4-8. Rhipidodendron Huxleyi, S. K., vol. i. p. 286. — 4, Detached ramuscule from 

 an adult branching zoothecium, x 170; 5, portion of branchlet, showing 

 quadruple tubular construction, x 300; 6, distal termination still more 

 magnified, showing contained monads, x 800 ; 7, diagrammatic illustration 

 of mode in which the characteristic branching zoothecium is produced, the 

 four primary monads, as at a, divided by longitudinal fission, the right and 

 left halves of such total product then parting, as at i, and forming their 

 respective tubules at divergent angles ; 8, symmetrically developed adult 

 zoothecium, x 5 ; 9, an adult zoothecium, natural size. 



