222 RAMBLES OF A NATURALIST. 



Beneden*, and others, that some of the hydroid 

 Polypes are merely the transitory forms which certain 

 Medusa} undergo before they arrive at their more 

 perfect state. 



It must not be supposed that this metamorphosis 

 can be compared to that of insects. In the latter, 

 each germ or egg produces a larva, which maintains 

 its special individuality through all its changes into 

 the grub, caterpillar, chrysalis, or butterfly. But 

 in the Radiata, the phenomena are very much more 

 complicated. The egg of the Medusa first produces 

 an ovoid, ciliated larva, very similar to certain of 

 the Infusoria. After having enjoyed its liberty for 

 a time, this larva becomes fixed, undergoes an altera- 

 tion of form, and gradually lengthening, is converted 

 into the stem of a hydroid polypary, from which 

 sprout, like so many leaves, an indefinite number 

 of well-characterised Polypes. After a time this 

 same stem produces new buds, which, instead of 

 presenting the form of Polypes, gradually assume 

 the characters of the Medusae. These buds or gem- 

 mules, which are at first adherent, become detached, 

 and finally appear as true Acalephae. Abandoning 

 their stationary brethren, they begin a wandering 

 life ; whilst the polypary from which they originated 

 continues to vegetate in its old place, and to throw 

 out new Polypes. Thus in the Radiata which we 

 have been considering, one sole germ, after having 



Amongst other works Sars is publishing a general treatise on the 

 Littoral Fauna of Norway, of which two parts have at present 

 appeared. 



* [A sketch of the scientific labours of Van Beneden is given in 

 the Appendix, Note XIII. ] 



