23 



numerous spicules in Sarcodictyon,"^ and united to form a 

 continuous tube in Tuhipora. t 



The four families forming the second series have been 

 differentiated in different directions, and differ from one 

 another mainly in their methods of budding to form colonies, 

 and in the kind of skeleton the}^ produce. The Helioporidge 

 are remarkable on account of their having twelve tentacles 

 and a peculiar corallum which shows certain resemblances to 

 the skeleton in the true corals or Madreporaria, a group with 

 which the HelioporidsB have no direct relationship. | In the 

 Alcyonidae the skeleton is in the form of scattered spicules, 

 while in the two remaining families, the Pennatulidse and the 

 Gorgonidae, a solid axis is formed which traverses the centre 

 of the colony. In the Pennatulidse the colony is of elongated 

 form, and the axis is unbranched ; while in the Gorgonidae 

 both are frequently of complicated and tree-like forms. 



The second diverging series of forms from the Proto- 

 polype, must have acquired the characteristic of having the 

 tentacles simple and in multiples of six, since those con- 

 ditions are found in the Antipatharia, and in nearly all 

 Actiniaria and Madreporaria. The ancestors of the Anti- 

 patharia probably were the first offshoots from the primitive 

 Zoantharia, and in their descendants at the present day we 

 find a form of skeleton developed which differs from that of 

 all other Zoantharia, and agrees with that of most Alcyon- 

 aria, in being an axial rod. The primitive Zoantharia must 

 then have split up into two series, of which one was the 

 stock of the Actiniaria, and the other of the Madreporaria. 

 The ancestors of the Sea-Anemones lost the habit of repro- 

 ducing by gemmation, and formed no hard skeleton of any 



* Herdman, «« On the Structure of Sarcodictyon," Proc. Roy. Phijs. Soc, 



Edin., vol. viii, p. 31 (1883). 



t Hickson, " On the Structure and Relations of Tubipora," Quart. Journ., 



Mic. Sc, vol. xxiii, No. xcii, p. 556 (1883). 



I Moseley, ** Challenger " Zoological Beports, vol. ii, part vii, p. 102. 



