CALCAREOUS SKELETON OF THE ANTHOZOA. 509 



taiuing two, three, or more nuclei ; where two sclerites are 

 formed in a single sclerohlast two nuclei are usually present, 

 and if only one sclerite is formed the nucleus apparently 

 divides when the sclerite has attained a certain size, and the 

 division is repeated as growth continues, without any corre- 

 sponding division of the cytoplasm. 



So far as the formation of the spicules is concerned, all that 

 is true of Alcyonium is also true of Gorgonia Cavolinii, 

 and these are the only two Alcyonarians which I have been 

 able to obtain in a living condition, and to preserve'^by appro- 

 priate methods. 



The spicules which I have examined belong to the smooth 

 lenticular, the spindle-shaped and scale-like warty kinds de- 

 scribed by Kolliker. 



The lenticular spicules were obtained from Clavularia 

 coerulea, Ehrh., and from Xenia and Ileteroxenia. In 

 Clavularia ccerulea these spicules are formed within ecto- 

 dcrunc cells, which do not migrate into the mesogloea. Each 

 spicule is of flat ovate shape, measuring some 002 ram. in its 

 longer and O'Ol mm. in its shorter diameter. These lenticular 

 simple spicules are remarkable for the large amount of organic 

 matter which they contain, an amount so great that, after 

 slow decalcification, the organic basis retains the shape and 

 size of the spicule, and can readily be stained by diffuse stains 

 such as hasraatoxylin or acid fuchsin. The undecalcified 

 spicule, when examined by the polariscope with crossed Nicols, 

 grows fainter in four positions at 90° to one another, but is 

 never wholly extinguished. This suggests that it is made up 

 of a number of crystals, the majority of which are parallel to 

 one another. In some few of the spicules I could detect signs 

 of a dark cross when the prisms are crossed, but this is only 

 an occasional phenomenon. In some specimens which had 

 been treated for a short time with very dilute acetic acid, I 

 could detect minute crystalline fibres which seemed to diverge 

 fan-wise from the centre towards the two extremities of the 

 oval spicule. But the structure is so minute that one cannot 

 see anything distinctly, even with an immersion lens. I can 



