TRACHYMEDUSjE LIRIOPE. 



415 



stomach-walls has taken place. The growth of the bell-walls causes the 4 original, solid, 

 radially placed tentacles to project from the sides of the exumbrella above the margin and 

 they usually break off and are lost. Before the loss of the 4 primary tentacles, however, 4 

 hollow, marginal tentacles grow out in the radii of the 4 radial-canals and 4 solid interradial 

 tentacles develop. The medusa thus develops 12 tentacles, only 8 of which are commonly 

 retained until maturity, although some individuals retain their 4 primary, radial tentacles 



Fig. 267.— A, B, C, Liriope mucronata, showing successive stages in growth of medusa from z to 

 10 mm. in diameter. D, Young Geryonia proboscidalis, 3 mm. in diameter. From life, by the 

 author, Zoological Station, Naples, December, 1907. 



until they are half-grown medusa?. To recapitulate, these 12 tentacles are: 4 original, solid, 

 exumbral, radially placed tentacles + 4 secondary, hollow, marginal, radial tentacles + 4 solid, 

 marginal, interradial tentacles. Mature medusa? are often found with only the 4 hollow, radial 

 tentacles remaining, the 8 others having been cast off. 



