242 CTENOPHORiE. Part II. 



it is easily ascertained to be out of place, owing to some accidental jjressure. 

 The variations which they undergo in their various degrees of contraction and 

 expansion having already been described when speaking of the movements of these 

 animals, I need not refer to the subject again. I have only to add, that they 

 appear frequently coiled up like a corkscrew, in a regular and more or less elon- 

 gated spiral. But, strange to say, in this position, though placed upon the two 

 sides of the body in a symmetrical position, the spiral is not antitrojjic, but coiled 

 in the same direction on both sides of the body, though their bases and hooks, 

 and, indeed, the Avhole upper part of their structure, shows a regular antitro2)ic 

 arrangement, like all symmetrical parts throughout the animal kingdom. Here, 

 however, I have constantly found the spirals of the thread, when coiled up, curved 

 in the same direction, jjoth of them turning to the left in an ascending direction 

 or to the right in the opposite direction. This is the more surjirising, as in 

 animals in which there are parts twisted upon the two sides of the bod}-, those 

 of the right side are curled in one direction, and those of the left side in the 

 opposite direction, in order to establish perfect sj-mmetry. Thus, the horns of 

 cattle, sheep, and goats are twisted, the right to the left, and the left to the 

 right ; while in antelopes the direction is reversed, the right horn being twisted 

 to the right and the left horn to the left. The same antitropy is also ob- 

 served in the bend of the tusks in elephants and wild boars, or of the horns 

 in deer, etc. Such an antagonism seems, therefore, not yet to prevail among 

 Eadiata, in which the anterior and posterior extremities have not become j^romi- 

 neiit. 



The lateral fringes have the same structure as the main thread, consisting, in 

 the middle, of a bundle of elongated cells surrounded b}' epithelial cells. When 

 contracted, the longitudinal cells, extending into the main thread, appear like 

 transverse fibres. There are, however, no transverse fil^res proper in the main 

 thread, any more than in the lateral fringes ; as in every instance those trans- 

 verse fibres of the main thread can be traced into the centre of the lateral 

 ones. The extension of the threads must therefore Ijc of a more passive char- 

 acter, owing to the relaxation of the fibres, and cannot be produced by the con- 

 traction of annular fibres ; though the longitudinal cells of the lateral fringes may 

 perhaps contribute by 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, b}' starts, the main thread seems 

 rather to be dropping 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 l^y 

 their structure the elongation of the lateral threads at ri^ht ausrles with the main 



