REPORT ON THE DEEP-SEA MEDUSAE. li 



figs. 5-8). The hollow tentacles are generally more flexible and movable, longer and 

 much more extensible, they are chiefly found in the Leptolinae (Antkomedusae and 

 Leptomedusse), and also in the majority of the Acraspedse. They contain a canal, which 

 represents a peripheric process of the gastrovascular system, and is lined by a single 

 layer of endodermal flagellate ceUs (PI. VII. fig. 4 ; PI. XVII. figs. 15, 16 ; PI. XXI. fig. 

 21, &c). In the two forms of tentacles, both solid and hollow, the endodermal axis is 

 covered by a structureless elastic supporting plate, which separates it from the overlying 

 muscular plate, and which at the same time acts as antagonist, or elastic extensor 

 against the contractions of the latter. The muscular plate consists of longitudinal 

 muscular fibrillar, which are usually still connected with the overlying epithebal muscular 

 cells of the ectoderm. The latter, moreover, contains thread cells and feeling cells very 

 variously arranged, and often also glandular cells and ciliated cells. 



§ 79. Organs of feeling (tactile organs, " organa palpantia "). As sensibility to 

 variations of temperature, and reaction against touch and pressure is wide spread among 

 the Medusas, tactile cells (" cellulse palpantes ") must necessarily be generally pre- 

 sent. All indifferent sense cells, all ectodermal cells with hair-shaped processes may 

 probably be considered as such. These tactile hairs may be either flexible and movable 

 (" flagellum ") or stiff and immovable (tactile bristle, " palpellum "). Whether all ecto- 

 dermal flagellate cells are to be regarded as tactile cells is still doubtful, but this view 

 probably holds good for the flagellate cells composing the sense-epithelium above the 

 nerve ring of the umbrella margin and the "marginal corpuscules," and also for the 

 flagellate cells, which in many Medusas form part of the outer epithebum of the ten- 

 tacles (sometimes arranged in longitudinal streaks, rings or spirals along the sides 

 of the tentacles, sometimes as a connected covering of the ends of the tentacles). 

 We appear more justified in considering these ectodermal flagellate cells as tactile 

 cells, when we perceive that their bases are directly connected with nerve fibrillar 

 This is also the case with the " cells with tactile bristles " of the ectoderm, which bear a 

 stiff, often long, and far projecting tactile hah', a tactile bristle or palpellum. Such cells 

 with tactile bristles are usually widespread in the ectoderm both on the exumbral dorsal, 

 and on the subumbral ventral surface, chiefly, however, on the most sensitive parts, on 

 the umbrella margin and the tentacles, and also on the oral margin and the oral arms. 

 According to this view, the whole urticating cells in the first place, and in the second 

 place the " tactile cells" in the more limited sense, or the palpocells (without nematocysts) 

 belong to this category. The " urticating bristle " (" cnidocilium ") of the urticating cells, 

 like the feeling bristle (" palpocilium ") of the actual " feeling cells," is a direct process of 

 the protoplasm of the cell, projecting externally freely into the water and as in both cases 

 the latter is connected at the base of the cell with nerve fibrillar, in both cases the stimu- 

 lation received by the palpellum can also be communicated by the nerves to other parts 

 (muscles, &c). The urticating cells (with cnidocilia and nematocysts) and the feeling 



