THE HYDROMEDUSAE 



colonial (Bougainvillea) ; but may be replaced by filiform pro- 

 cesses (Corymorpha) ; it is, of course, absent in the motile 

 forms (Hydra). In the colonial forms it gives rise to one or 

 more simple (Perigonimus) or branching (Bougainvillea) hydrocauli. 

 The coenosarc of both hydrocaulus and hydrorhiza generally forms 

 a single tube. 



Kio. ii;. 



Fio. n 



10 —Dia'nim sliowiiiK I'ossibli- inodilications of persons of a Oyjiiiioblastic llyclroineilusa. 

 a liyilrocaiilus (stem) ; /<, liyihorhiza (root); r, cocleiiteron ; (/, oiulodi'iiii (thick black line); 

 t' ectodprin (li.itehe.i) ; /, perisarc (thin black linp); ;;, hyilioid expanded; .;', hydroid con- 

 tracted- h, hyiPost.Miie, beurinn mouth at its extremity; h; dejjenerate niediisoid (sporosac) 

 spriii'dil;; tvi<u\ llie hvdriicauhis ; /,', sporosac springing from m, a modilied hydroid (blastoslyle) ; 

 the grnitlilia jire seeii sunoiiiiding the spadix ; /, me<lnsoid ; in, blastosfyle. (Alter Allman ) 



17 — DiaRram showing possible modilications of the persons of a Calyiitoblastu- Uy.iro- 

 medusa. Letters ii to k same as in Fig. 10. i, the horny cup or hydrotheca of the hydroid ; /, 

 niedusoid springing from m, a modified hvdroid (blastostyle); n, the horny case or gonotheca 

 enclosing the blastostyle and its buds. This and the hy<Irotheca i give origin to the name 

 CalyptoblasU'a. (After Allman.) 



The tul)cs of the hydrorhiza arc generally distinct from one 

 another, although tliey are often connected by cross-tubes into a 

 loose meshwork. In Podocorync, however, such a mcshwork occurs 

 only at the growing points of the colony ; in the more central parts 

 the tubes increase in number and anastomose so freely as to appear 



