220 



ZOOLOGY 



capacity for regeneration, as it is called, is seen also in 

 man when a wound heals, and a diseased organ, even when 

 partly destroyed, is made whole again. 



APPENDIX TO CHAPTER XIV 



KEY TO THE PRINCIPAL SUBDIVISIONS OF THE CNIDAKIA 



c*i. Body composed of 4, 6, or many rays ; nettling 

 organs well developed. 



61. Mouth at apex of an oval cone ; cavity 



simple . . . . . . Class 



Ci. Existing for the most part in 2 forms ; 

 a sessile one, hydroid ; and a free- 

 swimming one, medusa. The hydroid 

 form is sessile ; the medusse are 

 mostly small, or may remain at- 

 tached to the hydroid . Order 

 C2. Free-swimming colonies composed of 

 hydroid and medusoid individuals 

 budded on a floating stem . Order 



6 2 . Mouth at bottom of an oral crater ; cavity di- 



vided by radial partitions. The more com- 

 mon forms are large jelly-fishes . Class 

 2 . Body composed of 2 radii, with 8 meridional 

 rows of plates of cilia ; nettling capsules modi- 

 fied to form adhesive organs . . Class 



Hydrozoa 



Hydromedusce 



Siphonophora 



(Portuguese man- 

 of-war, etc.) 



8cyphozoa 



Ctenophora 



(Sea-walnuts) 



KEY TO THE FAMILIES OF THE HYDROMEDUS^ 



a\. Hydroid individuals, without cuticula or stolons ; 

 fresh water . . . . ... 



a 2 ' Hydroid individuals, if present, with cuticula or 

 stolons; marine. 



Hydroidm 



(Ex. Hydra) 



