ALCYONIUM STELLATUM. 



65 



the composition of the polypary, at which point its thickness is con- 

 siderably augmented, its texture spongoid, and in its substance are de- 

 posited a number of irregular crystals, composed of carbonate of lime, 

 mixed with a little colouring matter. In the tegumentary mass thus 

 formed the vascular canals ramify, anastomosing freely among them- 

 selves, so as to constitute a vascular network. These vessels are formed 

 of very attenuated membrane of a yellowish colour, which is continuous 

 with the internal tunic of the polyps, and is perfectly distinguishable 

 from the dense tissue with which it is surrounded. The distribution 

 of these canals is best displayed by cutting a thin slice of the mass of 



Fig. 28. 



1 2 



1 & 2. Sections of Alcyonium stellatum. 3. Ovigerous membrane of the same, isolated. 



the Alcyon, and removing the crystals with which it is filled by im- 

 mersion in some dilute acid ; it is then seen that the canals are most 

 numerous and of the largest size towards the extremities of the branches 

 of the polypary, and that they establish frequent communications be- 

 twaen the abdominal cavities of the different polyps of the Alcyon. 

 The fluids with which their bodies are filled must thus necessarily 

 circulate in the entire mass of the polypary ; and if each of the polyps 

 has, on the one hand, an individual sensibility and a distinct digestive 

 cavity, on the other there is a vascular system common to them all. 



(142.) The Alcyons, like the Alcyonides, are reproduced by ova, 

 which are formed in membranous ovaria of precisely similar construc- 

 tion ; and also by gemmae, which are developed around the pre-existent 

 polyps, and thus augment indefinitely the number of individuals united 



