THE MICROSCOPE

Evening Star, Issue 19352, 11 September 1926, Page 22

THE MICROSCOPE

SOME OF ITS WONDERS / PLANT OR ANIMAL? A QUESTION OF BOUNDARIES [Written by G. A. Rawsok, for the ‘Evening Star.’] (Concluded.) No. XL Close to the minute aperture which serves Euglena as a mouth there is a tiny dot of a bright crimson hue, commonly called an “ oye spot.” However, there is a difference of opinion among xnicroscopists as to whether this is really an organ of vision or not. Probably the name has been misapplied, although the late P.. H. Gosse, F.R.S., thought it very possible that by means of this organ the creature was sensible of a difference between light and darkness. A clear space surrounds this “eye spot,” while tho mass of the body, as already stated, is a bright translucent green, closely resembling vegetable matter. We are noi here dealing with a case of Symbiosis or organic partnership, such as occurs with Hydra, because the green color is not due to independent greon algie living in the body of Euglena, but is due to minute granules of chlorophyll. Strictly speaking, no vegetable has a right to a mouth, and no animal to chlorophyll. But Euglena possesses both. Nor does the crimson pigment spot solv« the difficulty. It looks extremely like an eye, but wo have yet to prove that it is more sensitive to light than the rest of the body. But the creature possesses one organ common to most Infusorians, which is called a contractile vacuole. This is a sort of expanding and contracting sac, which gets rid of surplus water and effete matter and is regarded as the forerunner of the kidney of tho higher animals. This contractile vacuole is distinctly an animal characteristic.

The simple truth is that in Englena wo find a combination of those characters which denote tho two primary divisions of organic life. The gulf between animal and vegetable, if _ such exists, is not here bridged by an intermediate form ; but the characters of the two co-exist side by side. Notwithstanding all this, the untrained observer who was viewing these curious organisms for the first time under the _ microscope would have no hesitation in declaring that they were animals. “ What else can they bo,” ho would exclaim, “ for here I can see an eye, a tail, and certain specks inside the body that appear to bo organs of digestion and reproduction?” But look a Little longer, -my friend, and you will see that some of them cease moving about and become more or less globular, while the tail disappears into tho body substance. Now they look more like vegetable organisms, such as are familiar to every microscopist who takes the trouble to examine water that has been exposed to tho air and sunshine for any length of time. Mr Gosse—no mean authority—was convinced that Eugleuso are animals, and Professor Niciiolson placed them among tho Infusoria, but admitted that they occupy a doubtful position. However, whether a plant or an our little Euglena is certainly one of the prettiest things that the student of the microscope can view, notwithstanding its proclivity for unsavory surroundings. In tho words of one charming writer, “ Even for thoso who have no desire to distract themselves with such intricacies as are suggested by the presence of chlorophyll and cellulose, the phenomena of respiration and the digestion of starchy and nitrogenous materials, or tho other secret processes which must be understood before any definition of plant or animal can lie arrived at, there is an almost endless fund of profit and delight in the examination of these minute organisms with the magic instrument which has brought within view whole worlds that were previously undreamed of.”

Aa already mentioned, the genus Euglena comprises several species. One such species is known as Eugleua sanguinea, so caDed because it is alleged to have been found of a deep red hue, and in such vast profusion as to tinge the water a blood red. It is an active little creature of about one 250th of an inch in length, very lively in its movements, and constantly altering its shape. Mr Gosse, however, states that he has never seen it other than a rich emerald green in the body, with the two extremities perfectly clear and colorless. Another species is known as Euglena acus, or the “ needle ” Euglena. It is a little larger than the former, but more slender and elongated. Its movements are comparatively slow and steady, and-hence it is more easily observed than some of its more versatile companions. “ This,” says Gosse, “is an animalcule of great elegance and brilliancy; its sparkling green hue, with colorless extremities, and its rich, pale crimson ‘eye’ are very beautiful.” When swimming, it usually extends itself, and moves through the water with a slow, graceful, gliding motion, rotating, on its long axis as it proceeds. It is able to bond its “ head ” and body in various directions, but looks at its best when fully extended. In this species we get a good opportunity of observing the red “eye-spot.” It appears to be a vacuole, or depression in the protoplasm, of an irregular, oblong shapej and filled with a clear, rubyred liquid. In the Rotifera, which are _ vastly more complex in tneir organisation than Euglena, the red spot is connected with a well-defined crystalline lens, of a high refractive power, which is an undoubted organ of vision, but in Euglena no such structure can be made out; the “eye-spot” has no definite fixed shape, and is not contained within a protecting membrane. In the well-stocked drop of water which wo are examining, we see two more species of this extensive genus. One is known as the “ Pear ” Euglena (E. pyrura), and the other as the “Sloth ” (E. deses). The former is'by faff the smallest we have yet seen, and is a highly curious and interesting creature. Its “ head ” end is somewhat protruded and truncate, and tho body terminates in a slender pointed tail. It is of a sparkling green color, but is clear at the tail and the edges of the body, and there is the usual bright red “ eye-spot.” Its,appearance under the microscope is most singular, because the body is obliquely fluted, and the. lines on the opposite side, owing to its transparency, are seen crossing those nearest the eye of the observer, thus dividing the creature into a num.ber of lozenge-sbaped areas. It swims with a swift gliding motion, turning continually jon its axis. This motion produces a pretty effect, a sort of waving irregularity, which is enhanced by the continual crossing of the fluted lines. We require a high power of the microscope to discern all these details in the creature for its length, including tho tail, is not more than one 700th of an inch I

i Euglena deses, besides being much larger—about one 250th of an inch in Idngth-Ms very different in shape. Its tody' 3 ' is thick, k and the “ head ” is round and blunt, while the tail is 7ory shorfci- Like all other members of this jcroup, its color is bright green, with

the red “ eye-spot ” well defined, but it is more opaque and blacker looking owing to the presence of a vast number of tiny, irregular granules,, and lines enclosing globular vesicles. It is a sluggish creature, and never moves gracefully or quickly among its more active companions, but seems contented to twine slowly in and out among the feathery filaments of water plants.