80 PKODUCTION OF POLYPS. 



first developed, are like little medusas or jelly-fishes 

 in shape, and have eight eyes, which are lost as the 

 animal attaches itself to some object. Sir J. G. 

 Dalyell, who had previously observed their forms, 

 states that the young, after the arms are formed, 

 advance by means of them, and being inverted, move 

 as on so many feet, apparently to select a site ; when, 

 again resuming the natural direction of the arms, 

 the lower surface fixes itself, and the animal becomes 

 rooted there for the whole time of its being. 



The polyp cells of Laomedia gelatinosa are 

 deeply cupped, transparent, with a wide even 

 margin. The vesicles are urn-shaped, and smooth, 

 shooting from the axils of the pedicles ; they are 

 matured during the summer months, " when," says 

 Dr. Johnstone, " we find them filled with ova of 

 a circular flattish form, marked with a dark speck 

 in the centre. At first they fill not more than half 

 of the vesicle, but by their increase in size, they 

 soon come to fill the whole cavity, and are ultimately 

 extruded from the top, after which the empty 

 vesicle soon disappears. The ova, while in the 

 vesicle, are arranged round a central column, and 

 the lid which closes the vesicle, is a mere expan- 

 sion of this column, which appears to be composed 

 of two pieces soldered together, where, perhaps, 

 the ova are more immediately affixed in their im- 

 mature state. . 



The polyps have about twenty long arms 

 roughened with minute tubercles, placed in whorls. 



