ON THE STINGING ORGANS OF MEDUSAE. 71 



external surface of the skin of the Medusa. I have observed in a very 

 beautiful and distinct manner the structure in the Pelagia noctiluca* 

 The outer skin is in that species of a beautiful brownish violet and 

 reddish colour on the convex discoid surface, on the exterior arched 

 edge of the arms, and on the lobes of the rim (Randlappen.) This varie- 

 gated membrane is easily separated, especially over the greater part of 

 the convex surface of the disc, and then there appears the homogeneous 

 jelly-like substance which constitutes the real body of the animal. 

 Where the red spots occur, we find, after the skin is detached, round 

 elevations or inequalities, like warts. 



By the assistance of a low magnifying power, the red spots appear 

 like collections of very small red grains of pigment, in whose vicinity the 

 whole body is covered by that kind of epithelium called a Pflasterepi- 

 thelium, consisting of larger and smaller cells, which contain distinct 

 nuclei. It is an epideimis analogous to that of the frogs and many 

 other animals. The accumulations of pigment occur especially on the 

 above-mentioned arched inequalities which arise above the surface, and 

 have a substratum of muscular fibres. 



Between the red grains of pigment are to be observed round balls 

 or bubbles, out of which frequently, by the aid of a strong magnify- 

 ing power (for this whole organization can only be recognised through 

 the microscope), fine threads are seen to project. The largest of these 

 balls present themselves as firm well-filled capsules of -^-th part of a 

 line in size, in which lies internally a spirally rolled- up thread, which 

 often comes out of itself, but always does so on the application of a 

 slight pressure. This thread then appears as a whip-like appendage to 

 the capsule, and has a very elegant outline. It is difficult to form an 

 idea of its structure : sometimes it seems as if it had a canal. When 

 the capsule is closed, while the thread is still rolled up in it, we per- 

 ceive an inequality to which the thread, when opened up, is attached, 

 as if to a stalk; when stretched out, the fine thread is a line long. 



These hair or thread capsules are very loosely attached, and easily 

 fall, and are rubbed off along with the slime, when the Medusa loses its 

 skin ; they are found in quantity, as are also the threads themselves, in 

 what is termed the stinging slime of the Medusas, (which is nothing else 

 but the cast off epithelium), as is easily ascertained when these animals 

 are kept in vessels. With more difficulty there are loosened smaller, 

 long- shaped, clear little capsules, from 3-5-0 th to z ^th of a line in size, 



The examination was made at Nice and Villafranca in the autumn of 1839. 



