ZOOPHTTEB. 383 



the general form, appearance, and habits, agrees with 

 the small naked-eyed Medusae, so closely, that if we 

 had not witnessed the birth of the little creature from 

 the reproductive cell of a Laomcdea, we should have 

 pronounced it with unhesitating confidence a true 

 Acaleph. The peduncle, it is true, seems out of place 

 being on the outside of the dome, instead of hanging 

 suspended from its interior ; but this difference is only 

 apparent, and arises from the circumstance that the 

 disk is reverted. If you suppose the edge of the disk 

 to be turned in the opposite direction, you will have 

 the peduncle in its normal place : the umbrella in these 

 specimens is carried M'ithin, and the sub-umbrella with- 

 out ; an inversion which is probably accidental. 



Comparing now this strange production of a Medusa 

 by a Polype, with what I lately told you of the pro- 

 duction of Polypes by a Medusa (as in the case of the 

 lovely little Turris), you will have some acquaintance 

 with the wondrous phenomena which have of late 

 years been surpi-ising and interesting naturalists — viz., 

 those of the Alternation of Generations ; in which as 

 Chamisso, the first discoverer of the strange facts, ob- 

 served — " a mother is not like its daughter, or its own 

 mothei", but resembles its sister, its grand-daughter, and 

 its grandmother." The Polype gives birth to a gene- 

 ration of Medusae which lay eggs, which develop into 

 Polypes. The Medusa on the other hand lays eggs 

 (gemmules), which develop into Polypes, which at 

 length divide themselves into colonies of Medusae. 



At first you will perhaps see nothing remarkable in 

 another object which I collected in my rock-ramble to- 

 day. A Hermit-crab in an old Natica. shell ; both 

 common things enough. Yet look more narrowly. 



