THE ANTHOZOA 19 



all parts of its lateral walls, with the exception of a short region 

 immediately beneath the tentacles. These solenia ramify in a much 

 thickened mesogloeal layer which is further strengthened by the 

 development of calcareous spicules, and lateral buds, which appear 

 to be direct offshoots from the elongated mother zooid, are formed 

 from the solenia. Some of the daughter zooids may in turn become 

 elongated and give rise to lateral buds, and so an arborescent 

 colony is formed, as in Coelogorgia. In the Pennatulids the cavity 

 of the mother zooid early becomes divided by a longitudinal 

 partition into two halves, and an axis of peculiar wood-like texture 

 is formed in the partition. The greatly enlarged and elongated 

 body of the mother zooid serves as the stem of the colony. In the 

 lowest Pennatulacea the daughter zooids are irregularly distributed 

 over the stem, in the higher forms they become symmetrically dis- 

 posed with regard to the stem, and tend to form rows, the members 

 composing which are fused together to form leaflets or pinnae. 



A fifth line of differentiation is found in the Helioporidae. In 

 these the solenia are not given off from the base, but ringwise at 

 about the middle of the length of the zooid, and immediately 

 beyond the zooid they anastomose so as to form a regular mesh- 

 work. From the nodes of the mesh work vertical solenial down- 

 growths are formed, and a dense calcareous lamellar skeleton is 

 formed from the ectoderm clothing the whole. Heliopora, the 

 single living representative of the family, is a peculiar and 

 aberrant member of the Alcyonaria, and will be described in detail 

 further on. 



The Synalcyonacea, according to the lines of divergence which 

 have been sketched out above, may be divided into six orders 

 whose relations may be expressed as follows : 



1. Stolonifera, Hickson. 



2. Alcyonacea, Verrill pro parte. 



3. Pseudaxonia, von Koch. 



4. Axifera, von Koch. 



5. Stelechotokea, Bourne. 



6. Coenothecalia, Bourne. 



We shall now proceed to review these several orders of the 

 Synalcyonacea. 



ORDER 1. Stolonifera, Hickson. 



Characters Colonial Alcyonaria with a root-like or membranous stolon. 

 Zooids either entirely free from one another except at their bases, or con- 



