486 
POPULAR SCIENCE REVIEW. 
consists of a single finger, the tip of which as a sharp curved 
point projects from the investing muscle, which here becomes 
globose. A delicately subtle rod which rises between the 
limbs of the V is the fulcrum of the lower jaws, seen at some 
distance forward, whose blades curve backward towards the 
beholder (as he looks at it dorsally) ; the whole being well 
imitated by the figure of the garden-shears. The blades, how- 
ever, are invested with thick globose masses of muscle, out of 
which the tips project, as the inferior pah of snapping points. 
It is the massive character of the muscular investments which 
during life so disguises the form of the apparatus ; and this 
massiveness, as well as the inordinate size of the whole structure, 
amounting to fully one-third of the entire bulk of the animal, 
indicates a predatory power which is by no means inconsistent 
with the impression of ferocity conveyed by the vigorous, 
sudden and frequently-repeated snappings, even when there 
seems nothing present to snap at. 
I have mentioned above the name of the genus Polyarthra. 
It is a member of this order, but -with peculiarities which 
isolate it from all others of the class. This, too, is a very 
difficult subject to make out, and it requires a long-continued 
study of the species, pursued through a great multitude of 
individuals, and a large acquaintance with other forms for 
comparison, well to understand its internal organization. This 
difficulty is augmented by its swift motion, its irregular fitful 
leaps, and its extreme transparency, combined with high 
retractile power. 
Its form is that of a crystalline cup, somewhat like the body 
of a wine-glass without any foot, but bearing many thin, 
sword-shaped processes, which proceeding from the breast 
commonly lie flat on each side down the body, the points pro- 
jecting below. These are evidently stiff and highly elastic, 
and their use is manifest to any one who sees the creature in 
active motion. It swims with a rapid gliding progress head 
foremost ; but at almost every moment it makes a sudden 
forcible jerk or leap backwards, or to one side ; and that so 
quickly, that the eye often cannot follow it in the transition. 
The organs by which these jumps are effected are the long 
breast-spines, which are suddenly thrown out in various direc- 
tions, and they may frequently be seen extended the moment 
after a leap, before they reassume their normal position. 
When we consider that the creature is jerked often four or 
five times its own length through so dense a fluid, we shall 
perceive how strong the muscular action must be which moves 
the lever-like spines. The creature is thrown irregularly, often 
with the side foremost, or the back, or made to perform 
a somersault in the act. It is probably a sensitiveness to 
