Royal Physical Society. 201 



and on the tips of the branchial papillae of Eolis. I am led to 

 conclude, therefore, that they are tactile prolongations of the 

 ectoderm, analogous to the prehensile processes of Actino- 

 phrys, or the long rays of Podophrya, and that their function 

 is probably to distinguish and seize the prey, and to convey the 

 stimulus necessary to effect the rupture of the death-dealing 

 thread-cells immediately beneath.* 



21. The Muscular Coat consists of a layer of closely-set, 

 ribbon-shaped fibres, passing upwards from the polypary to 

 the tips of the tentacles, so as to form a continuous tunic be- 

 tween the endoderm and ectoderm more transparent than, 

 either. It shows no indications of transverse strise ; but it 

 exercises considerable depolarizing power on polarized light, — 

 a property possessed by both striated and unstriated muscular 

 fibre. There can be little doubt that all the tissues of the polyp 

 have the property of slow contractability ; but the muscular 

 tunic appears to be specially adapted for the quick withdrawal 

 of the polyp body between the sheltering spines of the 

 corallum. 



22. The Endoderm of the polyp is a finely-granular opa- 

 lescent tissue, darker by transmitted light, and whiter by re- 

 flected light, than the ectoderm. Its appearance differs so 

 remarkably in various polyps of the same polypary, that the 

 observer might, with Quatrefages, be induced to represent it 

 as a compound of many different tissues. In its simplest 

 form, as it generally occurs in the reproductive polyps, it is a 

 structureless membrane, similar to the ectoderm, deeply loaded 

 with coloured granular matter, and ciliated on its internal 

 surface. In other polyps the endoderm is extensively vacuo- 

 lated, or filled with cavities, until it appears to consist of a con- 

 geries of cells of every variety in size. In a third class, 

 again, the vacuolation is still more extensive. Here the mem- 

 brane has the appearance of being split into two layers, one 

 of which forms an intestinal tube, occupying the axis of the 

 body, while the other lines the muscular tunic ; the two being 

 intimately connected by an areolar network of fibres, or septa, 



* As these processes have not heen hitherto noticed, I propose to distinguish 

 them by the appellation of " palpocils." 



