20 Coelenterata. 



radiate accordingly.- Besides these large ova there are in each medusa several 

 oocytes which stain more deeply, these are ultimately absorbed into the substance 

 of the large ova. The thick vacuolated eudoderm of the manubrium is a special 

 adaptation for affording nourishment to the maturing ova, its function resembles 

 that of the trophodisc of Stylasteridae. The margin of the umbrella presents 3 or 

 4 thickenings due to clusters of nematocysts but there are no tentacles nor sense 

 organs. The ripe ova found in liberated medusae are 0,25 mm in diameter. The 

 germinal vesicle is large but ill defined and has little chromatin. Zooxanthellae 

 are present in the vacuolated cytoplasm of the ovum. The free medusae (observed 

 in Jamaica by Duerden) are sluggish and pulsate feebly only now and then. The 

 ova are extruded and the medusa then shrinks and dies. It probably does not di- 

 gest food or nourish the ova after its escape from the ampulla. Certain cells in 

 the coenosarc of M. previously regarded by the author as ova are really the cells 

 which ultimately give rise to the larger nematocysts. 



