THE HYDROMEDUSAE 



FIG. 20. 



FIG. 21. 



Fio. 22. 



20. Part of colony of Pcrigonimus ; the thin perisarc 

 not shown. The zuoi'ls spring from a hydrorhiza. a, 

 hydroids in different phases of expansion ; b, developing 

 hydroid ; c, stages in development of medusoid ; d, free 

 inedusoid. (After All man.) 



21. Diagram of Clava, showing a hydroid surrounded 

 by a verticil of degenerate medusiform persons (sporosacs). 

 (Alter Allman.) 



22. Diagram of Hydractinia, showing four forms of 

 persons, a, hydroid ; li, modified hydroid, or blastostyle, 

 bearing c, degenerate medusiform persons or sporosacs ; 

 d, modified hydroid situated at the margin of the colony 

 (dactylozooid). (After Allman.) 



23. Diagram of Corymorpha, a hydroid with a double 

 circlet of tentacles. A, the hydroid ; ft, medusoids, 

 budded on its disc. 7>, the free medusoid, with one 

 tentacle ; the generative cells are indicated in the wall of 

 the nianubriuiu. (After Allman.) 



FIG. 23. 



