XXIV 



INTRODUCTION. 



stance and sends forth laden with the seed of new com- 

 monwealths. 



The free sexual zooid, with two or three exceptions, 

 assumes the form of a medusa, and is furnished with a 

 contractile swimming-bell or umbrella, by whose rhyth- 

 mical contractions it is propelled through the water. 

 (Woodcut, fig. xi. a.) 



From the centre of the crystal dome is suspended a hollow 



Fig. xi. 



body (the manubrium, Woodcut, fig. xi. 6), terminating at 

 the free extremity in a mouth, and at the point of attach- 

 ment in communication with a number of radiating tubes 

 or canals (Woodcut, fig. xi. c), which pervade the substance 

 of the umbrella, extending to its margin, where they join 

 a circular canal that connects them all (Woodcut, 



