342 CONTRIBUTIONS TO THE NATURAL HISTORY 



the right, and the left horn to the left. The same is also the case with the bend of tusks 

 in elephants and wild-boars, of the horns in deer, &c. Such an antagonism seems, 

 therefore, not yet to prevail among Radiata, in which the anterior and posterior ex- 

 tremities have not become prominent. 



Plate V. gives some further details of the structure of these tentacles. The main 

 thread, a portion of which is represented in Fig. 1, consists of elongated muscular 

 fibres, among which the nuclei of their primitive cells are sometimes still preserved, 

 as seen in Fig. 8. The surface of the thread is covered by several layers of epithelial 

 cells, among which, however, I have noticed no great differences in form and size, and 

 I have also failed to discover lasso-cells among them, though these tentacles are endowed 

 with an intense power of nettling, as they strike dead almost instantly any small Euto- 

 mostraca which come within their reach. 



As shown in Fig. 1, the lateral fringes arise uniformly from the same side, and where 

 one is occasionally seen in a different position, it is easily ascertained that it is out of 

 shape, owing to pressure when placed under the microscope. These lateral fringes have 

 the same structure as the main thread, consisting of a bundle of elongated fibres in 

 the middle surrounded by epithelial cells. The longitudinal fibres, however, extend into 

 the main thread, where they appear like transverse fibres. There seem, however, to 

 be no transverse fibres proper to any of the lateral fringes, nor even to the main thread, 

 as, in every instance, I could trace those transverse fibres of the main thread into the 

 centre of the lateral ones. The extension of the threads must, therefore, be of a more 

 passive character, owing to the relaxation of the fibres, rather than produced by the 

 contraction of annular fibres. The longitudinal fibres of the lateral fringes, however, 

 may probably contribute in their contraction to the elongation of the main thread. 

 This disposition explains very fully the slow elongation of the tentacles, in comparison 

 with their quick and almost instantaneous contractions, and also the peculiar phenomenon 

 attending this elongation, when, by starts, the main thread seems rather to be dropped 

 from point to point to its fullest elongation, in a passive way, by the relaxation of the 

 fibres. I am, however, at a loss to explain by their structure the elongation of the 

 lateral threads at right angles with the main thread, when this is fully expanded, and 

 their various dispositions, their frequent straight and apparently stiff elongation, and, 

 still more, their sudden bending even in acute angles. These motions are so diversified, 

 and sometimes so sudden, as to astonish even those familiar with the movements of these 

 animals. 



Having described above the position and changes of form of the digestive cavity, I have 

 now only to add, that its inner surface has not throughout the same appearance, and is 



