CNIDAKIA 



83 



the stolons do not belong exclusively to the basal part of 

 the polyps, bnt arise at various levels. In this way the 

 peculiar colony of Tubipora (Fig. 36 C) arises by the de- 

 velopment of stolonic plates in higher positions, from which 

 new buds grow out. In other forms, by the intimate fusion 

 and irregular branching of the stolons, there is developed an 

 intermediate tissue (coenenchyma) traversed by numerous 

 nutritive canals (Fig. 36 D), which unites the diiferent indi- 

 viduals. In this way the antler-like colonies of Alcyonium 

 are developed, and by the formation of a mesodermal axial 



Fig. 36.— Diagrams of budding and stock-formation in the Alcyonaria (-ifter 

 V. Koch, from Lang's Lehrhuch). A, formation of the basal stolon ; B, type of 

 the Gorgonidffi ; C, type of Tubipora ; D, type of Alcyonarium ; s, oesophagus; 

 se, septa ; in/, mesenterial ridges ; dh, gastral cavity ; sfc, axial skeleton growing 

 upwards by means of successive layers. 



skeleton the more slender forms, such as Corallium, Scleor- 

 gorgia, Melithsea, etc. (v. Koch). 



The development of colonies by budding is of special 

 interest in those forms in which, owing to the regular orien- 

 tation of the daughter individuals to the parent polyp, there 

 is established a regular bilaterally symmetrical structure of 

 the entire colony (Pennatula, Renilla). In these forms a 

 well-marked polymorphism of the individuals is exhibited, 



