THE HYDROMEDUSAE 



Fio. 20. 



Fig. -Jl. 



Fi<:. i-l. 



20. — Part of colony of Perigonimits ; the thin perisaic 

 not shown. The zooiils spriiif; from a hydrorhiza. n, 

 hydroids in different jihasps of ex]>ansion ; h, developing 

 hydroid ; c, sta^^es in development of medusoid ; il, free 

 niedusoi<l. (After Allman.) 



21. — Diagram of Clam, showin}; a hydroid sun-oundcd 

 by a verticil of degenerate medusiforni [lersons (sporosacs). 

 (After Allman.) 



22. — Diagram of Hydractinia, showing four forms of 

 persons, n, hydroid ; h, modified hydroid, or blastostyle, 

 bearing c, degenerate medusiforni persons or sporosacs; 

 tl, modified hydroiil situated at the margin of the colony 

 (dactylozooid). (After Allman.) 



23. — Diagram of Corymorpha, a hydroid with a double 

 circlet of tentacles. A, the hy<lroiil ; h, niedusoids, 

 budded on its disc. II, the free medusoid, with one 

 tentacle ; the generative cells are indicated in the wall of 

 the manubrium. (After Allman.) 



Fio. 23. 



