516 



DEVELOPMENT OF MEDUSAE FROM POLYPES. 



convulsive struggle ; it becomes detached, and swims freely away ; 

 and the same series of changes takes-place from above downwards, 

 until the whole pile of disks is detached and converted into free- 

 swimming Medusae. But the original Polypoid body still remains ; 

 and may return to its polype-like and original mode of gemmation 

 ( d, e ), becoming the progenitor of a new colony of Strobilce, every 

 one of which may in its turn bud-off a pile of Medusa-disks. 



423. The bodies thus detached have all the essential characters 

 of the adult Medusae. Each consists of an umbrella-like Disk, 

 divided at its edge into a variable number of lobes, usually eight ; 

 and of a Stomach, which occupies a considerable proportion of the 

 disk, and projects downwards in the form of a Proboscis, in the 

 centre of which is the quadrangular Mouth (Fig. 280, a, b). As 



Development of Medusa from detached gemmpe of Strobila : — 

 a, individual viewed sideways, and enlarged, showing the Pro- 

 boscis a, and b the bifid lobes; b, individual seen from above, 

 showing the bifid lobes of the margin, and the quadrilateral 

 Mouth ; c, one of the bifid lobes still more enlarged, showing the 

 rudimentary Eye (?) at the bottom of the cleft ; d, group of 

 young Medusae, as seen swimming in the water, of the natural 

 size. 



the animal advances towards maturity, the intervals between the 

 segments of the border of the disk gradually fill-up, so that the 



