THE FLEXIBLE CREEPERS. 
487 
danger or annoyance that prompts these violent leaps ; at 
least it frequently performs them after a momentary examination 
of any floating matter with which its course brings it into 
contact. 
This very remarkable animal deviates in several particulars 
from the rest of the order, and yet I think its affinities are 
with them. It has no semblance of a foot, and the investiture 
of the body forms a stiff' shell ( lorica ), as we find in the follow- 
ing order. Yet this is very peculiar. The back appears to 
me to be covered with longitudinal plates, divided from each 
other, and crossed by very delicate, close-set lines [striae). 
These plates appear to extend round to the ventral surface, 
protecting about one-third of the width on each side, and 
rising into a strong lateral point. The central third is occupied 
with membrane, which along the breast between the lateral 
points is rigid and shelly, but becomes quite flexible and skin- 
like towards the hind extremity. 
The sword-like fins are exceedingly curious and quite 
unique; for though a genus named Triarthra is furnished 
with three long spines, by which it performs leaps, yet the 
structure of these organs is very different from that of the 
swords of Polyarthra, and the animaPs affinities are with 
another order. These appendages are exquisite tests of the 
powers of the microscope, as well as of the skill of the observer. 
They are twelve in number, arranged in groups of three each, 
one group being set on each side of the dorsal, and one on 
each side of the ventral aspect, near the base of the projecting 
points of the breast. They are jointed, quite independently, 
on rounded shelly knobs, and are moved by strong muscles. 
Under graduated pressure I have brought out the four series 
of knobs, and the twelve fins with perfect distinctness, and 
have proved that the connection is that of true proper 
joints, like those of the limbs of insects. This existence of 
true joints, which is found in several other species of Rotifera, 
is one of the characters, on which I rely in maintaining, con- 
trary to the opinion of Mr. Huxley and other excellent 
naturalists, the high place of the class in the natural system. 
The fins are what botanists would call linear -lanceolate ; 
very thin, with a midrib running throughout, acutely (in one 
case that I observed, rather abruptly) pointed, distinctly 
toothed along each edge, the teeth pointing forward. Their 
texture is excessively delicate, and shows oblique lines running 
to the notches ; yet they are firm and highly elastic. 
The female carries its eggs, after they are discharged, 
attached to her body for some time ; another particular in 
which the species agrees with the Brachionidce. The young 
student must, however, be on his guard against a very natural 
