IS DEVELOPMENT OF 



afterwards as growing filaments, and in this way while 

 the interspaces continue to increase, the border of the 

 disc becomes furnished with long, pendent, prehensile 

 tentacles, which are very flexible and in continual motion 

 in all directions (fig. 30) ; and it is in this way that the 

 tentacles are formed. Simultaneously with the appear- 

 ance of these organs, the vessels of the disc become more 

 numerous, since from the arches or from the annular 

 canals formed by the arches, caecal vessels shoot out into 

 the substance of the disc, which increasing in length, inos- 

 culate with each other, and terminate in the radiating 

 canals which pass from the marginal corpuscles of the 

 lobes, (figs. 31 — 33.) At this period, the disc exter- 

 nally, exactly resembles the full-grown Medusa. 



The mouth, which even in the youngest detached 

 animal allows of being greatly extended and protruded, 

 is quadrangular, and presents four extensible angles. 

 These angles grow more rapidly than the four-sided oral 

 tube, so that in the more advanced animals, the mouth 

 appears during the growth, to have been divided or split 

 into four lobes. The minute serratures which appear on 

 the edges of these lobes are the commencement of the 

 lobes and fringes which are observed on those organs in 

 the adult animal. 



Our small Medusa, of about an inch in diameter, cor- 

 respond in their form, in all respects with those which 

 are fully grown ; as they increase in size, the internal 

 organs are developed, especially those destined for the 

 function of reproduction ; and their development is com- 

 pleted late in the summer, when the ova in the female 

 are fertilized, from which the infusoria-like fry proceeds, 

 which affixes itself, and assumes the polype form; whence 

 a new series of Medusa-larva, &c., and the whole of the 

 above-described development is repeated in the course of 

 the year. 



After having considered the particular course of de- 

 velopment of these Medusa, (and of the Medusa in 



