MATTHAI— RECENT COLONIAL ASTR^ID^. 



11 



brought forward further evidence in support of Hertwig's suggestion. My observations 

 on nematocysts in coral polyps lead to the same conclusion. 



Type I (PL 1, figs. 2, 3, PL 4, fig. 35, PL 6, figs. 63 and 65). This is the so-called 

 " tentacular type." It occurs not merely in the tentacles but in the edge-zone, oral-disc, 

 ectodermal ridges of the stomodseum and in the straight regions of the mesenterial 

 filaments (rarely in their coiled regions). There is no doubt, as Gardiner has shown, that 

 Bourne mistook nematocysts of this type in Euphyllia glabrescens for immature stages 

 of a totally different type, the so-called " mesenterial." A fully developed nematocyst 

 consists of a long narrow sac somewhat trumpet-shaped, widest at its upper end and 

 gradually narrowing towards its base ; the wall of the sac appears to be an elastic 

 membrane against whose inner surface lies a slender spirally-coiled filament stained dark, 

 the turns of the spiral being somewhat oblique and its number variable in the different 

 species from fifteen up to fifty. Even under the highest magnification (Zeiss Oc. 12 xob. 

 homog. immers. 2 '5 mm.), I have not been able to detect a spiral round the filament as in 

 type III described below. It merges at the bottom of the sac into a little granular 

 mass. Usually from the base of the sac a slender process passes down which, in the 

 unextruded nematocysts could be traced to the mesoglaea, possibly neuro-muscular, for 

 keeping the nematocyst in position and for the conduction of nervous stimuli. Normally, 

 the nematocysts lie with their upper ends touching the surface of the ectoderm, but, 

 when brought into action, are extruded partly or wholly with the filament ejected but 

 never seen completely uncoiled. The nematocysts attain to their full size only in the 

 tentacular ectoderm, where they are closely arranged to form batteries, elsewhere being 

 shorter with fewer turns of the spiral and never forming batteries. 



This type of nematocyst appears to be derived from an ectoderm nucleus. The 

 nuclear membrane grows in size to form the elastic wall of the nematocyst; within it the 

 chromatin-mass breaks up into minute granules (one of the granules in the middle of 

 the sac is conspicuous by its large size), which, by their union, form the coiled filament. 

 As the nematocyst grows in length the turns of the spiral are added to from above 

 downwards. The filament after it has attained its full length terminates in the residue 

 of the chromatin left at the bottom of the sac. The filamentar process passing from the 

 nucleus to the mesoglsea becomes the neuro-muscular process of the nematocyst. In the 

 tentacular ectoderm a nucleus, as it becomes modified, migrates towards the surface of 

 the layer, hence between the row of fully formed nematocysts at the periphery of 

 a battery and the small round nuclei just above the mesoglsea there are various 

 intermediate stages in the development of this type. According to this interpretation 

 every ectoderm-nucleus may be regarded as potentially capable of taking part in the 

 formation of a nematocyst. 



Gardiner, from his study of Ccenopsammia, has given a totally different interpretation 

 of the history of his " tentacular " nematocysts. He regards them as entirely cytoplasmic 

 in origin, the filament being formed by the union of granules in the protoplasm, resembling 

 "both in its development and appearance the elastic fibres in the connective tissue of 

 vertebrates," and states that "no nucleus can in any stage be distinguished within this 

 (nematocyst) membrane," but that " generally the basal end of the nematocyst lies in 



