40 



Invertebraia. 



depending from the centre of a large disk or umbrella 

 varying from an inch to three feet in diameter. The 

 mouth of the polypite is surrounded by lobate tenta- 

 cles (fig. 24), and from the stomach there pass eight 

 or more branching radial canals which are united 

 peripherally by a circular canal. The eggs are pro- 

 duced in pouches of the stomach-cavity, and each of 

 these on ripening emits a ciliated germ like an infu- 

 sorium (fig. 24 b\ which after a brief locomotory 

 existence settles down on some solid body at the sea 

 bottom (c\ and develops a hydra-like animal with 



FIG. 24. 



Medusa aurita in different stages of life ; a perfect adult form reduced ^ ; 

 b, c, d hydra-like stage; e,_f strobila stages ; g one of the disks separated 

 from./; and growing into adult form. 



branching canals which, elongating, forms a little 

 rooted colony (//). Each of these hydra-like forms 

 becomes marked with transverse furrows (e) which, 

 deepening, dip into the interior of the body dividing 

 it into a vertical 'pile of saucers/ of which each dis- 

 coidal segment becomes free as a new medusa. This 

 is a good example of alternate generations. 



