198 



CCELENTERATA. 



zooids of the colony, while the interlaminar spaces are filled with 

 the soft ccenosarc. The surface of the skeleton is covered with 

 projecting wart - like tubercles, interspersed with larger pointed 

 spines (fig. 79, b and c), these being really the upper projecting 

 ends of the "radial pillars." The surface also shows (fig. 79, b) the 

 rounded pores which lodged the zooids, together with singular 

 branched grooves or open canals, which apparently serve for the 

 lodgment of processes of the ccenosarc. In the living species of 





OOTGOfoGMdG^ 



Fig. 79. — a, A colony of Hydractinia />iioccena, attached to the shell of a Gastropod, of the 

 natural size, Pliocene. B, Portion of the surface of the same enlarged, showing wart-like promin- 

 ences, branched ccenosarcal canals, and minute circular zooidal apertures, c, Vertical section of 

 the crust of the recent Hydractinia cchinata, showing surface-tubercles and spines is). The suc- 

 cessive laminae of the skeleton (/, /) are separated by " interlaminar spaces " (z) which are broken 

 up into irregular chambers by "radial pillars." d, Vertical section of the crust of Hydractinia 

 cchinata, greatly enlarged, showing its composition out of vertical processes ("radial pillars") 

 united by horizontal bars or "arms" (c). e, Horizontal section of the same, showing the pillars 

 (/) and their connecting-processes (c), greatly enlarged. (After Allman, Carter, and the Author.) 



Hydractinia the organism consists of the general crust-like ccenosarc, 

 and of a large number of "polypites" emitted from the surface of 

 the same. Many of these polypites have mouths and tentacles, and 

 are devoted to the nutrition of the colony ; others are non-tentacu- 

 late, and carry sac-like generative buds, which are not detached 

 from the parent-colony ; while others form long spirally coiled fila- 

 ments, apparently intended for defensive purposes. 



The recent species of Hydractinia are all marine, and the skeleton 

 is in general composed of chitine ; but in an African species, de- 



