The Origin and Transformation of Animals. 101 



viviparous ; that they came into the world in the shape that they 

 preserved all their lives ; and that, strange to say, a solitary 

 mother only brought forth infants united in colonies, and these 

 in their turn engendered only solitary individuals. It followed 

 from this that a Salpa never resembled its mother or its son, 

 but always its grandfather or its grandson." Upon this 

 curious state of things, M. Quatrefages remarks that " me- 

 tamorphosis here influences generations and not individuals, 

 and matters proceed as if the caterpillar, instead of becoming 

 transformed, gave birth to complete butterflies, which in their 

 turn reproduced the caterpillars." 



It is, in fact, a case of the alternation of generations, the 

 precise nature of the process being left for Krohn, Huxley, 

 Leuckhart, and Yogt to elucidate. Before completing this 

 curious story, let us follow M. Quatrefages, and advert to a 

 similar set of incidents in the domestic manners of the Medusae, 

 or jelly-fish. " For more than a century," as he tells us, 

 zoologists had admitted among the other great divisions of the 

 sub kingdom of the Kadiata, the class of Acalepha, or medusa (sea 

 nettles, jelly-fish), and that of polyps. This distinction seemed 

 more than justified, as differences between the two groups were 

 detected, more profound, and more numerous than those which 

 separate the reptiles from the birds. There was in fact no 

 resemblance in external aspect or internal organization. The 

 jelly-fish, or Medusas, for example, are free swimmers, and 

 mostly solitary; while only a few polyps enjoy a crawling 

 motion, nearly all are fixed, and most of them live in colonies. 

 Notwithstanding these and other differences, the two classes 

 approximated as their history became known. " The medusa 

 lays eggs, well characterized by the existence of three concen- 

 tric spheres, of which we have already spoken. These eggs 

 transform themselves into larvae, which at first differ little from 

 those of the Serpula or the Teredo. Their oval and apparently 

 homogeneous bodies are covered with vibratory cilia, and 

 exhibit a small depression in front. They swim for some time 

 with vivacity, like the infusoria, which they resemble sufficiently 

 to deceive any one whose observations were restricted. This 

 first phase of the life of a Medusa lasts about eight and forty 

 hours. The movements then grow slower, the young larvae seem 

 fatigued, and by the aid of the little depression attach them- 

 selves to some solid body. Henceforth the wanderer vegetates 

 in one spot — a thick mucous which it secretes forms a large 

 disk that fixes it firmly.* The young Medusa changes its 

 shape as well as its mode of life. It elongates rapidly. Its 



* In a note M. Quatrefages says that lie has reproduced the opinion of Sars, 

 although he thinks it probable that the so-called mucous is a veritable expansion 

 of the sarcode. 



VOL. II. — NO. II. I 



