Page:The Cornhill magazine (Volume 1).djvu/76

drop of the liquid we find in it is placed on a glass slide, covered with a small piece of very thin glass, and brought under the microscope. Now look. There are several things which might occupy your attention; but disregard them now to watch that animalcule which you observe swimming about. What is it? It is one of the largest of the Infusoria, and is named Opalina. When I call this an Infusorium I am using the language of text-books; but there seems to be a growing belief among zoologists that the Opalina is not an Infusorium, but the infantile condition of some worm (Distoma?). However, it will not grow into a mature worm as long as it inhabits the frog; it waits till some pike, or bird, has devoured the frog, and then, in the stomach of its new captor, it will develop into its mature form: then, and not till then. This surprises you? And well it may; but thereby hangs a tale, which to unfold—for the present, however, it must be postponed, because the Opalina itself needs all our notice.

Observe how transparent it is, and with what easy, undulating grace it swims about; yet this swimmer has no arms, no legs, no tail, no backbone to serve as a fulcrum to moving muscles: nay, it has no muscles to move with. 'Tis a creature of the most absolute abnegations: sans eyes,

Fig. 1.

A B

Opalina Ranarum.

A Front view }
             } Magnified.
B Side view }

Fig. 2.

Group of Vorticella Nebulifera, on a Stem of Weed, Magnified.

A One undergoing spontaneous division.

B Another spirally retracted on its stalk.

C One with cilia retracted.

D A bud detached and swimming free.