HALF AN HOUR WITH CORALLINES. 



103 



with it. Agassiz has described a large umbrella- 

 shaped jelly-fish (Cijanea arctica), whose disk 

 measured seven feet across, and whose tentacles 

 were above fifty feet long, and yet this was produced 

 from a little coralline not more than half an inch in 

 height when full grown ! Few, however, of the 

 meduseans produced from the corallines reach this 

 enormous size, but they make up for it by their 

 countless myriads, which people every wave. Only 



Fig. 55. 



a. Lafcsa dumosa, natural size. 6, Polyp cells of the same, mag. 

 c. Young Sertularian Medusa, from Lafcea. 



one species of Sertularia (rugosa) is known to produce 

 meduseans, the usual method of reproduction in 

 this group being already explained. This was called 

 Lafoea dumosa (Fig. 55) by Lamouroux, and it was 

 termed by Professor Edward Forbes the most active 

 polyp he ever saw. When the generation buds, to 



