PLATE XXI. 



TUBULARIA LARYNX. 



FlOS. 



1. A hydranth from a male colony, with its long simple racemes of gonophores ; magnified. 



2. A hydranth from a female colony, with its shorter compound racemes of gonophores ; 



magnified. 



3. An entire colony, natural size. 



4. A portion of the hydrocaulus, showing the interrupted annulation of the perisarc ; slightly 



magnified. 



5. Summit of stem much magnified, showing the fluted collar-like expansion, a, of the 



ectoderm. The perisarc is continued from a point at a little distance below the collar as 

 a thin filmy and transjjarent tube over the distal portion of the stem. 



6. An actinula some days after its liberation, as it is seen floating in the surrounding 



water ; magnified. The oral tentacles, which are absent at the period of liberation, have 

 already become developed. 



7. The actinula after it has permanently fixed itself. It has developed a stem which is clothed 



with a chitinous perisarc, and has emitted hydrorhizal processes of attachment. The 

 young stem is excavated into a single cavity instead of being traversed by several longi- 

 tudinal canals, as in the corresponding stage of Tiibidaria uidivim. Very distinct 

 currents are visible through the transparent walls of the stem, as indicated ])y the arrows 

 in the figure. 



