OF THE ACALEPHiE OF NORTH AMERICA. 341 



that along the vertical chymiferous tubes which arise towards the upper end of the ten- 

 tacular cavity, there are on each side linear edges slightly swollen in their middle, and 

 thinner below, but curved over the middle of the disk from above, where they unite ; 

 then, descending somewhat lower, they are detached from the outer surface of the disk, 

 to meet on their lower margin a similar fold rising from below, and then hang downwards 

 into the bottle-shaped cavity free, as an independent thread, surrounded as soon as 

 it is free from the disk by numerous small elastic and contractile tentacles. The main 

 thread, however, forms the stem of the tentacle, which is capable of an extraordinary 

 development, and can also be contracted into a coiled bundle ; so that, in the state 

 of utmost contraction, it forms a sort of irregular ball of tuberciilated appearance 

 hanging from the hook, the tubercles of the surface being the lateral fringes ; but 

 when elongated, it is changed into a fine thread, and the fringes appear at intervals, 

 either in a contracted or elongated form, assuming, in the former state, the ap- 

 pearance of little tubercles, which in tlicir elongated condition are themselves like 

 so many little threads. In Fig. 1 and 5 of Plate IV., as well as in Fig 5 of Plate 

 III., the tentacle being in its state of elongation, the lateral threads are distant from 

 each other. Their arrangement in this part of the tentacle, however, is not easily 

 ascertained ; but when expanded, or regularly contracted within moderate limits, we 

 cannot fail to see that they all arise from one side of the main thread, and are 

 throughout unilateral. The variations which they undergo in their various degrees of 

 contraction and expansion having already been described, when speaking of the move- 

 ments of these animals, I need not refer to the subject again. I shall only mention 

 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 antitropic, but coiled in the same 

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

 whole upper part of their structure, show a regular antitropic arrangement, like all sym- 

 metrical parts throughout the animal kingdom. Here, however, I have constantly found 

 the spirals of the threads, when coiled up, curved in the same direction, both of them turn- 

 ing to the left in an ascending direction, or to the right in the opposite direction. This 

 is the more surprising, as in animals in which there are parts twisted upon the two sides 

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

 are curled in the opposite direction, thus establishing perfect symmetry ; and this law of 

 nature is imitated in architectural ornaments, to produce complete symmetry. 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 



