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 



a\. Body composed of 4, 6, or many rays ; nettling 



organs well developed. 

 b\. Mouth at apex of an oval cone ; cavity 



simple Class 



c\. Existing for the most part in 2 forms ; 

 a sessile one, hydroid ; and a free- 

 swimming one, medusa. The hydroid 

 form is sessile ; the medusae are 

 mostly small, or may remain at- 

 tached to the hydroid . Order 

 c 2 . Free-swimming colonies composed of 

 hydroid and medusoid individuals 

 budded on a floating stem . Order 



62- 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.) 



Scyphozoa 



Ctenophora 



(Sea-walnuts) 



KEY TO THE FAMILIES OF THE HYDKOMEDUS.E 



i. Hydroid individuals, without cuticula or stolons ; 

 fresh water . 



2 - Hydroid individuals, if present, with cuticula or 

 stolons; marine. 



Hydroidw 



(Ex. Hydra) 



