174 REVIEWS—CONTRIBUTIONS TO NATURAL HISTORY. 
of its specific gravity and that of the water in which it lives. So Pleurobrachia 
may appear at times, and so does it also appear when moving in a state of con- 
traction. But generally, when active, it hangs out a pair of most remarkable 
appendages, the structure and length, and contractility of which are equally 
surprising, and exceed in wonderful adaptation, all I have ever known among 
animal structures. Two apparently simple, irregular, and unequal threads hang 
out from opposite sides of the sphere. Presently these appendages may elongate, 
and equal in length the diameter of the sphere, or surpass it, and increase to two, 
three, five, ten, and twenty times the diameter of the body, and more and more; ~ 
so much so that it would seem as if these threads had the power of endless 
extension and development. But as they lengthen they appear more complicated, 
from one of their sides other delicate threads shoot out like fringes, forming a row 
of beards like those of the most elegant ostrich feathers, and each of these threads 
itself elongates till it equals in length the diameter of the whole body, and bends 
in the most graceful curves. These two long streamers, stretching out in straight 
or undulating lines, sometimes parallel, then diverging or variously curving, 
follow the motions of the main sphere, being carried on withit in all its move- 
ments, which are no doubt influenced by them to a considerable extent. Upon 
considering this wonderful being, one is at a loss which most to admire, the 
elegance and complication of that structure, or the delicacy of the colours and 
hues, which, with the freshness of the morning dew upon the rose, shine from its 
whole surface. Like a planet round its sun, or, more exactly, like the comet with 
its magic tail, our little animal moves in its element as those larger bodies revolve 
in space, but unlike them, and to our admiration, it moves freely in all directions ; 
and nothing can be more attractive than to watch such a little living comet as it 
darts with its tail in undetermined ways, and revolves upon itself, unfolding and 
bending its appendages with equal ease and elegance, at times allowing them to 
float for their whole length, at times shortening them in quick contractions and 
causing them to disappear suddenly, then dropping them as it were from its 
surface so that they seem to fall entirely away, till, lengthened to the utmost, they 
again follow in the direction of the body to which they are attached, and with 
which the connection that regulates their movements seems as mysterious as the 
changes are extraordinary and unexpected. For hours and hours I have sat before 
them and watched their movements, and have never been tired of admiring their 
graceful undulations. And though I have found contractile fibres in these thin 
threads, showing that these movements are of a muscular nature, it is still a unique 
fact in the organization of animal bodies, that parts may be elongated and con- 
tracted to such extraordinary and extensive limits by means of muscular action.” 
We must bring this notice to a conclusion. We cannot speak too 
highly of the merit and interest of the work, or of the beauty, effec- 
tiveness and usefulness in conveying information of the numerous 
plates which accompany it. The work has met with liberal patronage, 
and neither author nor publisher has spared any pains to deserve it 
both by the originality and value of the matter, and by the sump- 
tuous manner in which it is brought before the public. W. H. 
