REPORT ON CORALS—HYDROCORALLIN &, 23 
seen, and also multiramified amceboid-looking corpuscles occurring in the endoderm (same 
ficure, RC), and resembling those figured by Allman as occurring in the tentacles of 
Coryne pusilla, and considered by him to be the nuclei of the large endodermal cells." 
The body-cavities of the zooids were observed in the living condition to be filled with 
the yellow pigmented cells, and a few of these cells were seen occasionally to penetrate a 
short distance into the cavities of the tentacles, which cavities are continuous by widely 
open mouths with those of the bodies of the zooids. Ciliation of the somatic cavities 
could not be seen. 
The spheroidal heads of the tentacles are composed of masses of closely-set 
nematocysts of various sizes and stages of development, but all of one peculiar kind 
(Pl. XIII. fig. 2), the larger ovoid nematocysts never occurring in them. <A thin 
hyaline, apparently structureless ectodermal layer extends between these agglomerated 
nematocysts, its marginal outline not being circular but depressed in short curves between 
the somewhat projecting tips of the cells (Pl. XIV. fig. 5). 
The gastrozooids, when retracted, viewed directly from above, show the mouth in the 
centre, and four, five, or six tentacles arranged at equal distances around. ‘The dactylo- 
zooids, when retracted, have their tentacles closely drawn together, so as to form a 
hemispherical mass composed of the closely-set spheroidal tips of the tentacles (Pl. XIV. 
figs. 2 and 3). It can easily be understood how a vertical section through such a mass 
of retracted minute tentacles would give the appearance of a large compound tentacle, 
the small tentacles appearing to constitute the pinnee. I was misled by such a prepara- 
tion; and in my paper upon Heliopora carulea, presented to the Royal Society,’ I 
stated my belief that the tentacles of Millepora would prove to be compound. 
The body-cavities of the zooids terminate inferiorly in blind ends at the bottoms of 
the calicles, but are continued outwards at their bases in all directions into the canals of 
the hydrophyton, which join them all around, being disposed in an irregularly radiate 
manner (Pl. XIV. figs. 2 and 6). 
Muscular fibres, having a longitudinal disposition, are extremely well developed in the 
zooids. They arise for the most part in bundles from the radiating vessels of the ecenosare, 
which spring from the bases of the zooids, and pass up the walls of the bodies of the 
zooids, extending in the gastrozooids nearly as far as the mouth. In the contracted 
zooids, when viewed directly from above or below, they have necessarily a radiate dispo- 
sition, as shown in Plate XIV. fig. 6. Not all the fibres are gathered into the bundles, but 
some sparsely spread ones occupy the interval between these bundles, maintaining a like 
radiate course. The bundles may be traced for a considerable distance along the radiating 
vessels. In vertical sections from osmic acid preparations the muscular elements can be 
observed as isolated excessively fine fibres (as far as was seen, without nucleus), which 
1 Allman, Gymnoblastic and Tubularian Hydroids, pl. iv. fig. 3. 
2 Phil. Trans., vol. elxvi., part 1. 
