ALTERNATION OF GENERATIONS, 



&C. &C. 



CHAPTER I. 



THE DEVELOPMENT OF THE MEDUSA. 



(ScyPHISTOMA-SxKOBIlA, MeDIJS^.) 



Tab. I. figs. 1 to 40. 



I presuppose tliat my readers are acquainted with the 

 animals vulgarly" termed "- jelly-fishes' or '■'■ sea-nettles^' 

 and in scientific language ''Medusa!' They are creatures 

 of a gelatinous consistence, very soft, and transparent as 

 glass, and are met with of various forms, discoid, hemi- 

 spherical, or bell-shaped, and they may be seen swimming 

 about immediately below the surface of the water, at sea 

 or in creeks, from spring till late in the autumn, but only 

 when the surface is tranquil and no rain has been falling. 

 They occur in vast numbers, especially where streams fall 

 into the sea or into a creek or bay, and they swim more 

 deeply in the water when the surface is rough, or after a 

 fall of rain, the slightest shower causing them to descend 

 rapidly. On the approach of winter they withdraw them- 

 selves to a greater depth, or probably nearly all die at 

 that period. 



The circular border of the disc or bell of the Medusa is 

 sometimes entire, and continuous without any division, 

 and sometimes presents teeth, lobes, or fringes. This 

 condition, however, varies very much in different genera, 

 and, as we shall soon see, does so remarkably even in 

 individuals of the same species, according to their dif- 



