THE ANTHOZOA 



27 



It always lies eccentrically in the coelenteron, and becomes fused ])artly 

 with the body wall, partly with the neighbouring mesenteries. Before 

 the axis has reached the level of the stomodaenm, the surrounding parts 

 of the primitive coelenteron become differentiated, and take on the char- 

 acters of solenia, which, as growth proceeds, become more differentiated 

 and distinct. At a later stage the distal moiety of the zooid is separated 

 by a constriction from the moiety which surrounds the axis, and thus 

 comes to look like an appendage of the stem. The first daughter zooid 

 is formed as an outgrowth of a solenium on the side of the axis ojiposite 



Fig XIV. 



1.— A colony of dorgonia Cavolitii, von Koch. (>nt»-<iuaitiT natural size. 



"2. — Extremity of a branch of Uorgonia Vavoliai, showing zooids in various stages of con- 

 traction. Magnified. 



3. — Optical section through the mother zooid of a colony of Oorgoniu Cavolini, showing the 

 formation of the axis, A , as a secretion of the basal ecto<lenn. 



4. — Optical section tlirough an older stage with two zooids. --I, axis. 



All the tigures after (i. von Koch. 



to the zooid already formed, and successive zooids are formed in the same 

 manner, alternately on either side of the axLs. In the fully grown 

 colony the cortex or coenenchyme consi.sts of a thickened mesogloea, in 

 which lie solenia, who.se course is mainly longitudinal, i.e. parallel to 

 the axis. In the smaller branches of some forms eight solenia are present, 

 which probably represent the eight inter-mesenterial chambers of the 

 primary zooid. In the main stem the number is usually greater. Tlie 

 solenia, both in stem and branches, anastomose freely with one another, 



