THE MEDUSiE. 35 



This mode of development it is true has been observed 

 only in Medusa aurita and Cyancea capillata, two of om" 

 most common species of Medusa, in which the earlier 

 circmnstances of development so entirely correspond, that 

 it cannot be determined whether any given nurse belongs 

 to one or the other ; but in all probability a similar mode 

 of development occurs in all true Medusa. It is, how- 

 ever, sufficient for our present piurpose that researches 

 have shown this mode of development to occur in certain 

 genera of the family. 



But with respect to the relation of the periods of de- 

 velopment to the seasons of the year, it should be re- 

 marked, that it is in the latter months of summer that 

 we meet with Medusa containing mature ova ; and that 

 the researches of Sars on the origin and affixing of 

 the fry, were made in September and October, whilst 

 the detachment of the Medusa-larva has been observed 

 in the spring months of March and April. In the 

 first half of summer, and until the beginning of July, 

 I found in the Atlantic, solitary, free swimming indi- 

 viduals of from I '" to 3-4 '" in diameter. If to this 

 we add the general observation made before, that the 

 smaller spechnens of Medusa are usually met with in 

 spring, and the larger in summer, we shall perceive that 

 the development of these animals, like that of the rest of 

 the organic world, is intimately connected with the peri- 

 odical motions of the globe. 



others, which make good their individuality at a later period ? May not 

 several of these gemmae originate in the same brood, which has attached 

 itself to an iadividual already afiixed a short time previously. 



