1847.] Alternation of Generations, etc., 225 



remarkable and until now inexplicable natural phenomenon of an 

 animal producing an offspring which at no time resembles its pa- 

 rent, but which on the other hand, brings forth itself a progeny, 

 which returns in its form and nature to the parent animal, so that 

 the maternal animal does not meet with its resemblance in its 

 own brood, but in the descendants of the second, third or fourth 

 degree or generation; and this always takes place in the different 

 animals which exhibit the phenomenon in a determinate number 

 of generations. 



The first instance which the author adduces as an example of 

 this kind of generation is the Medusce, an animal which is soft 

 and like jelly, and frequently in the form of an umbrella with fin- 

 gers dependant from the margin. They are well known animals, 

 especially to those who reside upon or frequent the sea shore. 

 They are also called sea nettles and jelly fishes. 



These beautiful and singular beings, which really are almost 

 entirely composed of sea water and seem to float almost at ran- 

 dom, bring forth their young in a condition capable of rowing 

 themselves about, and form at the proper time, swarms, which at 

 this period are quite distinct in form from the parent. They are 

 small and in shape like a slightly compressed cylinder, though larger 

 atone end, and covered over with ciliaj, which serve to row them 

 about. In swimming the large end is forward, and as it is fur- 

 nished with a depression it would be taken for the oval aperture. 

 But the observer is soon led to correct this mistake, as it soon 

 plants this end downward when it becomes permanently attached; 

 it is to be regarded as a suctorial disc. When this attachment is 

 formed, the other end presents a small orifice. This end soon en- 

 larges and a border is formed around the upper extremity, and in 

 the course of five or six days there shoots out from the border 

 tentaculaj or arms. In this state it closely resembles a polypi. 

 In process of time, eight tentaculffi are formed. After this the 

 number increases and they continue to spring up until they amount 

 to thirty. When the full number of tentaculffi are attained a new 

 kind of life manifests itself. At equal distances along the soft 

 pulpy body, wrinkles begin to appear, which, extending trans- 

 versely, form a channel with a distinct border, and with an edge. 

 From this edge again arms shoot out, in form and shape like 

 those which first appeared upon the young medusa, when it be- 

 came fixed. It now appears like a series of fringed cups set into 

 each other. Each of those little fringed discs or cups become vi- 

 talized, and when the process of separation is completed, each 

 fringed body becomes a distinct individual and rows itself about 

 upon its own hook. The state in which these individuals now 

 are, is that of a young medusa, and in process of time, and by 

 growth each individual detached as described above, becomes a 



No. 19. 18 



