Chap. I. HISTOLOGY OF CORYNE MIRABILIS. 207 



view {Fiff. 12, a}). The innermost wall {Figs. 10, b, and 14, c) is papillate on its 

 inner surface [Fk/s. 10, h, 13, a b, and 14, c^), owing to the slightly projecting ends 

 of the cells. The cells (PI. XIX. Fig. 14'') are much smaller than those of the 

 outer wall, and also differ in having distinct granular contents, a smaller mesoblast 

 {h), not granulated, and a much more conspicuous, but smaller, dot-like, dark ento- 

 blast {c). 



When the medusa is fairly free from the restraint of the horny sheath, and 

 has had a few hours to expand itself, the individual cells of the different walls 

 are found to have dilated considerably. The cells which compose the outer wall 

 of the disk and its transverse septum, are in one layer, excessively transparent, 

 and very difficult to recognize. They are usually six-sided (PI. XIX. Fig. 22), and 

 nearly symmetrical, with smaller and fainter mesoblasts [a) than those of the last 

 phase, and mere dot-like entoblasts {b). An extremely faint granulation pervades 

 the whole cell. Freshwater swells these cells {Fig. 21), and causes the granu- 

 lation to vanish, but does not seem to affect the mesoblasts. At the base of the 

 tentacles, the outer wall of the bulb (PI. XIX. Fig. 26) is a solid mass of very 

 transparent, small, rounded cells, hardly larger than the mesoblasts of the disk cells 

 {Fig. 22). The surface of this bulb is covered by large lasso-cells {Fig. 25). The 

 outer wall (PI. XX. Fig. 9, c) of the tentacles is more transparent than the outer 

 wall of the disk, and does not afford the least trace of cellular structure, except 

 in the case of the lasso-celLs {b), which are imbedded in heaps within its thick- 

 ness. A few scattering cylindrical papillte («) give a peculiar appearance to the 

 tentacle at this age, but they disappear very soon. By plunging a fully-grown 

 medusoid into freshwater, the cellular structure of the i-adiating tubes was brought 

 out very clearly. In profile (PI. XIX. Fig. 27, b), the wall presents only a single 

 layer of broad and short cells, closely resembling those of the inner wall of the 

 tentacles. Each cell contains a single, moderate-sized mesoblast. Viewed in front 

 (a), these cells appear polygonal, and much broader transversely to the axis of 

 the tube. The middle wall of the disk shows no trace of organization, beyond 

 the parallel horizontal strite (PI. XIX. Fig. 24), Avhich have been pointed out in 

 the last phase. In this case, they were seen in a natural state, and appear to 

 be wider apart than when heretofore noticed. Where this wall is continued into 

 the proboscis (PL XIX. Figs. 15, h^ h^ h, and 16, Jr' h), and constitutes its inner 

 wall, the cellular structure is very easily discerned. In the pendent part of the 

 proboscis {Figs. 15, h h^, and 16, h), the cells are very large and transparent. In 

 profile they are seen to vary in shape, according to the degree of contraction or 

 expansion of the proboscis; sometimes having a broad cylindrical shape {Fig. 16, h), 

 or, at another time, being prismatic and conical {Fig. 15, h), with the apex inward, 

 forming the inner surface of the cavity of the proboscis, and the broader end 



