284 CONTRIBUTIONS TO THE NATURAL HISTORY 



funnel. I suppose these very great changes in its form (for it is generally stretched hor- 

 izontally) are brought about, in a great measure, by the action of the muscular fibres 

 which arise from the chymiferous tubes, and run obliquely downwards. (Plate III. Fig. 3, 

 g g, Fig. 4, g, g, h.) 



The appearance of the muscular tissue in this animal, as studied under high magnify- 

 ing powers, varies somewhat in different parts of the body. Wherever the tissue can 

 most easily be traced in its intimate structure, scarcely a doubt can be left that the 

 muscular fibres are elongated cells. Indeed, in the horizontal partition, it is as plain as 

 possible. The whole tissue appears like layers of elongated, or rather caudate cells, with 

 one end blunter than the other ; and the nucleus near the larger end now and then 

 contains a nucleolus. These cells are in such juxtaposition as their heterogeneous form 

 requires to fill the whole space, the blunt end being sometimes in one direction, and 

 sometimes in the opposite direction, and the attenuated part of the cells packed more or 

 less closely together, so as to leave no empty space between, as is seen in Plate III. Fig. 

 11, or in Fig. 10, where they are more fully metamorphosed. These latter cells appear 

 almost entirely thread-like, though the nuclei are still preserved. In the large vertical bun- 

 dles, however, the approach to ordinary muscular fibres is nearest, inasmuch as few nuclei 

 remain between the threads. But one circumstance distinguishes such muscles completely 

 from any of the muscular structures of higher animals : there is nowhere any indication of 

 transverse striae upon the fibres ; there are no sarcous elements, nothing like that reticulat- 

 ed structure of true muscles which has been observed in the higher animals. The condi- 

 tion of the voluntary contractile system of Medusae comes nearest to that of the unstriated 

 muscles of higher animals. Indeed the aspect of the true voluntary muscles of Hippo- 

 crene almost reminds us of the figures of unstriated muscle given by KoUiker. 



IDEAL SECTIONS. 



Though the figures to which I am about to refer cannot claim the merit of extreme 

 precision, they will at least contribute somewhat to an understanding of the results to 

 which I have arrived respecting the structure of this animal. I have therefore thought it 

 useful to introduce them, in order that all the parts, which I have above described in their 

 natural relations, may be thus represented more definitely than they are really seen in 

 nature. 



Plate VIII. Fig. 1, gives merely an outline of the gelatinous disk in a vertical sec- 

 tion. It will be noticed here, that its inner lower surface, instead of being simply arched, 

 has a central rounded prominence, a ; that the thickest part of the vault, b, is above 

 the main cavity ; and that the lateral walls, c, gradually taper downward into a narrow 



