234 CEYLON PEARL OYSTER REPORT. 



proportion of these nematocysts in D. gracilis present this appearance ; but others 

 may be found in which a thick thread loosely wound in a spiral of few turns is 

 clearly distinguishable, and it is scarcely open to doubt that the forms filled with 

 granular material are simply unripe. In fig. 27c I have drawn a nematocyst of this 

 variety which seems to throw some light on the development of the thread. In the 

 centre of the capsule is the pointed end of the thread (much longer than in 

 Coenopsammia) surrounded by a granular sheath which seems to be differentiating to 

 form the eversible portion of the capsule. At the base of the capsule the granular 

 sheath widens out and forms a rounded mass in which an irregularly and imperfectly 

 formed coil can be distinguished : this I take to be the middle portion of the thread 

 in course of formation. Near the point of the thread, and outside the granular 

 sheath surrounding it, is a spiral of five turns closely wound round the granular 

 sheath : this must be the terminal portion of the thread differentiated from the 

 granular sheath at the same time that the latter gave rise to the eversible portion 

 of the capsule. The capsule itself is lined by a rather thick granular layer. It 

 should be observed that in these nematocysts the terminal part of the thread is 

 wound round the eversible sheath near the aperture for the extrusion of the latter. 

 Gardtner (loc. cit., plate xxxiv., fig. 14) figures it at the opposite end of the 

 capsule, but in Coenopsammia the eversible sheath is only one-third the length of the 

 capsule. In DendrophylUa, moreover (von Heider agreeing with me in this), there 

 is a distinct spearhead-shaped tip to the thread, as in Euphyllia, whereas Gardiner 

 found no such armature in Coenopsammia. 



In the "batteries" of the tentacles there are, as usual, very numerous and closely 

 crowded nematocysts of the small spiral variety, and among them a considerable 

 number of the second variety described above, which, if Gardiner is right, are to be 

 regarded as early stages of the spiral variety. I think, however, that they are really 

 a different form of nematocyst. I was able to distinguish a fine fibril passing inwards 

 from the bases of many of the small spiral nematocysts, and in some cases I could 

 observe that this fibril passed into a fine layer of protoplasm surrounding an oval 

 nucleus, and that from this a fine branching fibril passed into the layer of nerve fibres 

 overlying the mesoglcea (fig. 27a). The ectoderm of the peristome is very thick as 

 compared with Heteropsammia and Heterocyathus, and contains a large proportion of 

 gland cells and the same nematocysts as the ectoderm of the body wall. The 

 stomodaeal ectoderm, as von Heider remarked, is composed almost exclusively of 

 elongated cells of the columnar type ; they are almost certainly ciliated, but the cilia 

 had been destroyed by the action of alcohol. There are few gland cells, those that 

 are present being of the flask-shaped finely granular type, in the stomodeeum and very 

 few nematocysts. All the nematocysts that I was able to recognise belong to the 

 second variety described above. 



The mesenterial filaments are crowded with gland cells and nematocysts, the latter 

 all of the same medium-sized variety as those of the stomodseum, and this fact leads 



