274 CONTRIBUTIONS TO THE NATURAL HISTORY 



tissue, and to be able to trace its numerous bundles in all their details, it is necessary 

 to watch specimens in a state of great contraction, when they are about dying, or shortly 

 after death, and even during the process of decomposition. The powerful contractile 

 bundles on the inner surface of the gelatinous disk, to which the most powerful action 

 during life must be ascribed, are best seen in those specimens which are rapidly dying 

 under spasmodic contractions ; — while the superficial layers outside of the gelatinous 

 disk are even better seen when the animal is already decomposing, and the tessellated 

 epithelium, which covers the whole surface, is either decaying or separating from the 

 body. The cells of the lower partition are easily observed in fresh specimens during 

 life, probably owing to the circumstance that this partition is much thinner, and con- 

 sists of finer organic elements. 



When examined under a powerful microscope, the superficial epithelium (Plate II. 

 Fig. 5, 6) is found to differ in different parts of the body, and it is advisable to be famil- 

 iar with it before attempting to investigate the muscular apparatus. All over the bell- 

 shaped part of the disk, this epithelium consists of irregular polygonal cells, the outlines 

 of which are so faint that they are hardly ever distinguished ; but their existence can 

 easily be inferred from the peculiar arrangement of their granular contents, which 

 form a sort of mosaic (Plate II. Fig. 5), circumscribed within angular outlines, in the 

 interior of which larger nuclei of irregular form are noticed, sometimes placed in the 

 centre of these areolae, sometimes nearer their outlines. The forms of these nuclei vary 

 also, being either ovate or circular, or elongated, straight or curved, or even angular. As 

 in the fresh state these parts are too transparent to be well distinguishable, and they only 

 become visible in a rather advanced state of decomposition, I am not perfectly sure 

 that this irregularity of form is entirely natural, and that the nuclei, in particular, have 

 so diversified an appearance as is observed in the shreds which are so easily detached from 

 the surface of the gelatinous mass during the decomposition of the body. But so much is 

 certain, that such a ragged appearance, and this greater irregularity of the nuclei, (Plate 

 II. Fig. 6,) are particularly observed upon the outer surface of the lower margin, where 

 the vertical portion of the disk is turning over between the colored buds to form the trans- 

 parent lower partition ; and it may be that the character assigned by Mertens to his 

 species, of having a kind of villosity around the margin, is owing to a greater irregularity 

 of the epidermal cells in that species than in the one which I have examined. Upon 

 the sides, however, and above the disk, as well as upon the inner surface of the main 

 cavity, I have only noticed those more regular polygonal and flat epithelial cells, the greater 

 number of which contain only minute granules, and occasionally among them a few larger 

 nuclei, the whole forming a very thin film over the entire surface of the body. The 



