XI. 



EXPLANATION OF FIGUEES. 



PAGE. 



Fig. 1. — An example of a small Hydroid colony 



(after Hincks) xvi. 



Fig. 2. — An Athecate, or naked polypite . . 34 



Fig. 3. — A Thecaphorean polypite provided with a 



horny covering, or receptacle . . . . 34 



Fig. 4. — The structure of a typical Hydroid {Hydra) 

 and the distinctive difference between Budding 

 and Ova production ; also a dart cell (from 

 Parker and Haswell after Schneider) . . 36 



Fig. 5. — Animal of Hydra vulgaris, showing young bud 



and mature bud ; also dart extruded from its cell 38 



Fig. 6. — Diagram to show the nature of " budding " 40 



Fig. 7. — Hydractinia echinata, showing "select" poly- 

 pite, reproductive buds, tentacular filaments and 

 horny spines. . . . . . . 42 



Fig. 8. — Shows a small crustacean pierced by darts 



of a Hydroid . . . . . . 44 



Fig. 9. — Shows a Thecaphore in which the receptacle 

 is produced into points, forming a roof or oper- 

 culum, over the polypite . . . . 46 



Fig. 10. — Eeproductive bud with oral tentacles, of 



Tubularia coronata . . . . . . 50 



Fig. 1 1 . — A typical Hydroid with its free Eeproductive 



bud, or Medusa . . . . . . 54 



Fig. 12. — Transverse section of polipary of Coppinia 

 arcta for correlation with crust of Hydractinia 

 (fig. 7), and the section of stem of Antennularia 

 (fig. 13) . . .. .. 64 



Fig. 13. — Transverse section of Antennularia ramosa 75 



Fig. 14. — A polypite of Plumularia pinnata expanded 

 and gorging a worm; also enlargements of 

 tentacle and dart cells in situ . . . . 78 



Fig. 15. — A polypite of Plumularia pinnata retracted, 



with " Nematophores " or " Guard " polypites 79 



Fig. 16. — Shows the change and atrophy which take 

 place in the "select" polypite in the course of 

 its evolution from the Athecate to the The- 

 caphoreap. form. Also the point where the fully 

 matured Medusoid fails to be set free . . 81 



