LUCERNARIJi] AND THEIR ALLIES. 15 



broad excavation ; and the other is when the umbel is thrown backward in such a 

 way that its posterior face is concave {Jjg. 1) and the proboscis projects conspicu- 

 ously from its convex anterior face. At times tlie umbel is arched so strongly 

 forward that the body has tlie form of a wide-mouthed trumpet [fig. 4), or still 

 more projected and narrowed it simulates the outline of a deep funnel (^fig. 7). 

 Yet near these two extremes of concavity and convexity of the front face there 

 are all possible means, as may be seen by consulting the several figures which 

 adorn the plate, representing this species at various ages. The highest degree of 

 contractility of which it is capable is exhibited by inrolling tlic edge of tlie umbel 

 so as to conceal the bunches of tentacles [fig. 15) and compacting itself into a 

 globose mass, but without retracting the caudal cylindrical portion more than 

 enough to give it a very broad columnar proportion {fig. 14), and never so much 

 as to merge it into the general mass. 



35. Locomotion. — The flexibility as well as the muscularity of the body is most 

 vividly presented when the animal is roving from place to place. It has been said 

 by continental observers that it swims like a pelagic medusoid, by alternately 

 contracting and expanding its umbel ; but although we have waded time and 

 again for hours among the eel-grass where they were so numerous as to almost 

 swarm, we have never once witnessed anything that could be compared to the 

 pulsating movement of the umbella of a genuine oceanic Acaleph. It is true 

 that we have seen these creatures detach tliemselves from their point of support, 

 but they exhibited no systematically concerted motions whicli would drive them 

 in any particular direction, and the whole process consisted in rapidly flexing or 

 jerking the body from one side to another, with an occasional rapid folding together 

 and unfolding of tlie opposite halves of the lunbel. It is possible that the swim- 

 ming faculty belongs to the H. octoradiata (Z. octoradiata, Sars, non Lamarck), 

 which has been so often and so long confounded with the species now under conside- 

 ration. The usual mode of locomotion is by a process of creeping or stalking over 

 bodies, after the manner of a Hydra, using as prehensible, or rather adherent, organs, 

 the discoid caudal termination and tlie eight oval, kidney-like bodies (anchors, 

 coUetocystophores, § 104) which spring from the edge of the umbel, one by one, in 

 the intervals between the clumps of tentacles. Rarely does this Lucernarian appear 

 to use the tentacles as instruments of rcptation, nor do they contain the adhesive 

 bodies which make up so largely the mass of the kidney-like organs and the 

 disciform truncation of the caudal end of the body. As the animal passes from 

 point to point, it swings itself backward and forward, at one moment barely 

 adiicrent by the edge of the caudal disk, and at the next, with an abrupt jerk, it 

 throws the margin of the umbel against some object and tilts over, using one or 

 two marginal liodies as aneJioi-ft whilst it detaches the former base of support 

 (fig. 13). In the latt(n- condition it shows at times a high muscular power, by 

 swimming abruptly from side to side, or with violent jerks and a sort of gyrating 

 motion it throws itself into rapidly succeeding and varied positions, th(> heavy 

 caudal region meanwhile whirling about in the watery space like a club in the 

 hand of a gymnast. 



