THE STRUCTURE OF XENIA HICKSONT. 259 



(PL 25, fig. 12, Cn.C), the nucleus and protoplasm of which lie 

 flattened against the capsule on one side and a little nearer 

 the inner than the outer end of the capsule. The filament or 

 thread lies coiled up inside this capsule, there being about 

 twelve coils distinguishable in the most favourable specimens. 

 Tlie thread appears to be quite simple, there being no barbs 

 visible. Its length when shot out would probably be about 

 80 ju ("08 mm.). The nematocysts are usually placed with 

 their long axes at right angles to, and their bluntly pointed 

 ends level with or slightly projecting from, the free surface of 

 the ectoderm. This can be especially well seen in sections of 

 the tentacles and pinnules (see fig. 11). The nematocysts 

 staindeeply with thionin,ha3matoxyliu, and especially with iron 

 hsematoxylin (Heidenhain). Iron hsematoxylin is exceedingly 

 useful for staining the small nematocysts of Alcyonaria; in 

 fact, without some good staining reagent it would be very 

 difficult to find the minute capsules in many cases. Moseley 

 (1881, p. 119) wrote that ''no nematocysts were found in 

 Sarcophy ton," but by using the iron heematoxylin stain I 

 have found them in sections passing through the ectoderm of 

 the tentacles. They are very similar in shape to those of 

 Xenia Hicksoni, but smaller in size, being only 6 /u to 7 )ii 

 long and 2 n wide. The nematocysts of Alcyonaria are all 

 very small, as may be seen from the following table : 



Spicules (PI. 25, figs. 13—15; PI. 26, fig. 16).— The 

 spicules, the form of which was compared by Kolliker to that 

 of red blood-corpuscles, are rounded or oval discs, which are, 

 however, sometimes bilobed (fig. 13). They are -012 mm, to 



1 S, pauciflorum, Ehreuberg = Lobophytum pauciflorum, v. 

 Marenzeller, ' Zool. Jahrb.,' i, 1886. 



