ACALEPH^. 225 



less, some naturalists have rather taken them for ears reduced to their 

 most simple expression. 



The Medusae are not absolutely destitute of nervous system. We 

 have seen that they have ganglions, and prohahly optic nerves. 

 Ehrenberg also states that they have ganglions at their base, which 

 furnish them with nervous filaments. 



Without entering further into the details of their delicate and com- 

 plicated structure, we shall pause briefly on their mode of reproduc- 

 tion. We shall find here physiological phenomena so remarkable as 

 to appear incredible, had not the researches of modern naturalists placed 

 the facts beyond all doubt. " Which of us," says M. de Quatrefages, 

 " would not proclaim the prodigy, if he saw a reptile issue from an 

 egg laid in his court- yard, which afterwards gave birth to an indefinite 

 number of fishes and birds ? Well, the generation of the Medusae is 

 at least as marvellous as the fact which we have imagined." Let us 

 note, for example, what takes place with the Eose Aurelia, a beautiful 

 Medusa, of a pale rose colour, with nearly hemispherical disk, from 

 four to five inches in diameter, whose edge is furnished with short 

 russet-brown tentacles ; taking for our guide the eloquent and learned 

 author of the " Metamorphosis in Men and Animals," M. de Quatre- 

 fages. 



The Medusa, designated under the name of Eose Aurelia, lays eggs 

 which are characterised by the existence of three concentric spheres. 

 These eggs are transformed into oval larvae, covered with vibratile 

 cells, having a slight depression in front. They swim about for a short 

 time with great activity, much like the infusoria, which they strikingly 

 resemble in other respects. 



At the end of forty-eight hours the movements decrease. Aided by 

 the depression already noted, the larvae attaches itself to some solid 

 body, fixing itself to it at this point by the assistance of a thick mucous 

 matter. A change of form soon takes place : it becomes elongated ; its 

 pedicle is contracted, and its free extremity swells into a club-like 

 shape. An opening soon presents itself in the centre of this extremity, 

 through which an internal cavity appears. Four little mammals have 

 now appeared on the edge, which are elongated in the manner of 

 arms. Others soon follow : these are the tentacles of a polyp : the 

 young infusoria has become a polyp ! 



The polyp increases by buds and shoots, just like a strawberry 



Q 



