3S 



INTRODUCTION TO ZOOLOGT. 



of food. The naraber of these arms increases until it reaches 

 twenty-four or thirty ; and the body, originally about the size 

 of a grain of sand, becomes a line, or the twelfth part of an 

 inch in length. The animal, in its free state, swims about in 

 the manner of the Polygastric animalcules ; in its present con- 

 dition, it presents an analogy to the habits of the Rotifera. 

 During the winter months, it remains in security, " where the 

 waves have no strife," and even throws out germs, or buds, 

 which in time become perfect Medusoe {Fig. 24). But, with 

 the approach of spring, the body becomes marked Avith trans- 

 verse lines (Fig. 25), which gradually assume a wrinkled or 

 furrowed appearance. These furrows become deeper, dividing 

 the body into from ten to fifteen distinct portions, which, for 

 a time, remain in contact, but without organic connexion, 

 " like piled-up cups"* Fig. 26). After complete separation, 



25. 



26. 



Development of the Medusa. 



each part swims freely about, presenting an appearance so 

 unique, that the young, in this state, has been figured and 

 described as belonging to a new genus {Fig. 27). 



The last change observable is its putting on the appearance 

 of the perfect animal, and under the influence of the sun, the 

 waves, and the currents, becoming a mature Medusa. " We 

 thus see," says Professor Owen, "that a Medusa may actually 

 be generated three successive times, and by as many distinct 

 modes of generation — by fertile ova, by gemmation, and by 

 spontaneous fission — before attaining its mature condition." 



Our admiration of the various functions performed by the 



• Such is the expression employed by Stcvnstrup in his I^Iemoir "on 

 the Alternation of Generations;" publislicd by tlie Ray Society, 1845 

 The facts and illustrations we give on the authority of Steenstrup, Sar3 

 and other di$tin<ruishcd naturalists. 



