12 PERCY SLADEN TRUST EXPEDITION 



a finely granular mass of protoplasm with a nucleus either oval or rod-shaped." I have 

 carefully examined the serial sections of his polyps of Coenopsammia and have found that 

 the appearances of the tentacular and oral-disc ectoderm in iron-hsematoxylin are 

 identical with those in my polyps. All the stages in the modification of a round nucleus 

 into a nematocyst can be made out. The nucleus in Gardiner's fig. 7 does not of course 

 belong to the nematocyst, but is simply one of the many nuclei in the ectodermal 

 syncytium. 



The Hertwigs (66) have given figures of nematocysts from Actinians which resemble 

 type I (PI. 2, figs. 12 and 13, PL 3, figs. 5 and 11). In PL 4, figs. 2 and 5, each of 

 these nematocysts is represented as arising in the cytoplasm of an ectodermal cell with 

 the nucleus lying by its side when it is fully developed. Jourdan (74) has recorded 

 nematocysts of the same type from the tentacular ectoderm of the Zoantharia he studied 

 (PL 3, figs. 10 and 11; PL 12, figs. 83—85). In PL 5, figs. 32—36 {Actinia equina) and 

 in PL 15, fig. 108 (Balanophyllia regia) he has figured cnidocils which I have not found 

 in my sections. The type of nematocysts which, according to van Pesch (111) is so 

 abundant in the tentacular batteries of Antipathides, is doubtless the same as type I 

 (PL 4, figs. 5 and 6).* 



Type II (PL 1, fig. 8, PL 2, fig. 18, PL 3, figs. 26, 33, 34, PL 4, figs. 37 a—/, 38, 

 PL 6, figs. 58 a and h, 59, and 62). The nematocysts belonging to this type are large 

 oval sacs, broad at one end and bluntly pointed at the other, found everywhere in the 

 ectoderm but principally in the convoluted regions of the mesenterial filaments, where 

 they may be closely arranged to form batteries. Each of these consists of a membranous 

 wall containing somewhat granular contents. A narrow cylindrical structure or axis 

 extends from the upper end of the nematocyst to about two-thirds its length. This 

 consists of a dark-stained axial core, usually straight, sometimes slightly bent, always 

 pointed at its outer extremity, and enclosed in a thin membranous sheath against the 

 inner surface of which lies a fine close spiral, also stained dark ; the sheath leaves the 

 pointed extremity of the axial core free. This type resembles in appearance the nemato- 

 cysts figured by Hadzi (59) from certain Hydromedusse, and by Boulenger (10) from 

 certain Craspedote Medusae. In a few cases I have noticed the pointed tip of the axis 

 projecting beyond the sac, but there is no further evidence of the protrusibility of this 

 nematocyst-organ in any of the polyps I have examined. The nematocyst attains its 

 full size in the convolutions of the mesenterial filaments, being smaller in the ectoderm of 

 the oral-disc and edge-zone. It usually takes up a position at right angles to the surface 

 of the ectoderm, the pointed tip of the axis slightly pushing up the ectodermal surface. 



In the tentacle, nematocysts of this type occur in the terminal batteries interspersed 

 among those of type I, but always in a modified form, being much narrower and somewhat 

 longer, and the axis not extending beyond a third of the length of the sac. In some of 

 these there is a faint suggestion of a coiled thread. This variety, owing to its constancy 

 in shape and distribution may be termed type II (PL 3, figs. 26 and 33). 



In the genus Goniastrea these nematocysts are much narrower and longer and the 



* The second type of nematocysts yellow in colour and without any spiral which van Pesch has observed in 

 the tentacular batteries of Eucirripathes rumphi may not unlikely be a variety of type II. 



