第 5 节
作者:猜火车      更新:2021-02-24 23:33      字数:9322
  Bridgman; and we have seen that when their attention is engaged;
  they neglect impressions to which they would otherwise have
  attended; and attention indicates the presence of a mind of some
  kind。  They are also much more easily excited at certain times than
  at others。  They perform a few actions instinctively; that is; all
  the individuals; including the young; perform such actions in
  nearly the same fashion。  This is shown by the manner in which the
  species of Perichaeta eject their castings; so as to construct
  towers; also by the manner in which the burrows of the common
  earth…worm are smoothly lined with fine earth and often with little
  stones; and the mouths of their burrows with leaves。  One of their
  strongest instincts is the plugging up the mouths of their burrows
  with various objects; and very young worms act in this manner。  But
  some degree of intelligence appears; as we shall see in the next
  chapter; to be exhibited in this work;a result which has
  surprised me more than anything else in regard to worms。
  Food and Digestion。Worms are omnivorous。  They swallow an
  enormous quantity of earth; out of which they extract any
  digestible matter which it may contain; but to this subject I must
  recur。  They also consume a large number of half…decayed leaves of
  all kinds; excepting a few which have an unpleasant taste or are
  too tough for them; likewise petioles; peduncles; and decayed
  flowers。  But they will also consume fresh leaves; as I have found
  by repeated trials。  According to Morren {18} they will eat
  particles of sugar and liquorice; and the worms which I kept drew
  many bits of dry starch into their burrows; and a large bit had its
  angles well rounded by the fluid poured out of their mouths。  But
  as they often drag particles of soft stone; such as of chalk; into
  their burrows; I feel some doubt whether the starch was used as
  food。  Pieces of raw and roasted meat were fixed several times by
  long pins to the surface of the soil in my pots; and night after
  night the worms could be seen tugging at them; with the edges of
  the pieces engulfed in their mouths; so that much was consumed。
  Raw fat seems to be preferred even to raw meat or to any other
  substance which was given them; and much was consumed。  They are
  cannibals; for the two halves of a dead worm placed in two of the
  pots were dragged into the burrows and gnawed; but as far as I
  could judge; they prefer fresh to putrid meat; and in so far I
  differ from Hoffmeister。
  Leon Fredericq states {19} that the digestive fluid of worms is of
  the same nature as the pancreatic secretion of the higher animals;
  and this conclusion agrees perfectly with the kinds of food which
  worms consume。  Pancreatic juice emulsifies fat; and we have just
  seen how greedily worms devour fat; it dissolves fibrin; and worms
  eat raw meat; it converts starch into grape…sugar with wonderful
  rapidity; and we shall presently show that the digestive fluid of
  worms acts on starch。 {20}  But they live chiefly on half…decayed
  leaves; and these would be useless to them unless they could digest
  the cellulose forming the cell…walls; for it is well known that all
  other nutritious substances are almost completely withdrawn from
  leaves; shortly before they fall off。  It has; however; now been
  ascertained that some forms of cellulose; though very little or not
  at all attacked by the gastric secretion of the higher animals; are
  acted on by that from the pancreas。 {21}
  The half…decayed or fresh leaves which worms intend to devour; are
  dragged into the mouths of their burrows to a depth of from one to
  three inches; and are then moistened with a secreted fluid。  It has
  been assumed that this fluid serves to hasten their decay; but a
  large number of leaves were twice pulled out of the burrows of
  worms and kept for many weeks in a very moist atmosphere under a
  bell…glass in my study; and the parts which had been moistened by
  the worms did not decay more quickly in any plain manner than the
  other parts。  When fresh leaves were given in the evening to worms
  kept in confinement and examined early on the next morning;
  therefore not many hours after they had been dragged into the
  burrows; the fluid with which they were moistened; when tested with
  neutral litmus paper; showed an alkaline reaction。  This was
  repeatedly found to be the case with celery; cabbage and turnip
  leaves。  Parts of the same leaves which had not been moistened by
  the worms; were pounded with a few drops of distilled water; and
  the juice thus extracted was not alkaline。  Some leaves; however;
  which had been drawn into burrows out of doors; at an unknown
  antecedent period; were tried; and though still moist; they rarely
  exhibited even a trace of alkaline reaction。
  The fluid; with which the leaves are bathed; acts on them whilst
  they are fresh or nearly fresh; in a remarkable manner; for it
  quickly kills and discolours them。  Thus the ends of a fresh
  carrot…leaf; which had been dragged into a burrow; were found after
  twelve hours of a dark brown tint。  Leaves of celery; turnip;
  maple; elm; lime; thin leaves of ivy; and; occasionally those of
  the cabbage were similarly acted on。  The end of a leaf of Triticum
  repens; still attached to a growing plant; had been drawn into a
  burrow; and this part was dark brown and dead; whilst the rest of
  the leaf was fresh and green。  Several leaves of lime and elm
  removed from burrows out of doors were found affected in different
  degrees。  The first change appears to be that the veins become of a
  dull reddish…orange。  The cells with chlorophyll next lose more or
  less completely their green colour; and their contents finally
  become brown。  The parts thus affected often appeared almost black
  by reflected light; but when viewed as a transparent object under
  the microscope; minute specks of light were transmitted; and this
  was not the case with the unaffected parts of the same leaves。
  These effects; however; merely show that the secreted fluid is
  highly injurious or poisonous to leaves; for nearly the same
  effects were produced in from one to two days on various kinds of
  young leaves; not only by artificial pancreatic fluid; prepared
  with or without thymol; but quickly by a solution of thymol by
  itself。  On one occasion leaves of Corylus were much discoloured by
  being kept for eighteen hours in pancreatic fluid; without any
  thymol。  With young and tender leaves immersion in human saliva
  during rather warm weather; acted in the same manner as the
  pancreatic fluid; but not so quickly。  The leaves in all these
  cases often became infiltrated with the fluid。
  Large leaves from an ivy plant growing on a wall were so tough that
  they could not be gnawed by worms; but after four days they were
  affected in a peculiar manner by the secretion poured out of their
  mouths。  The upper surfaces of the leaves; over which the worms had
  crawled; as was shown by the dirt left on them; were marked in
  sinuous lines; by either a continuous or broken chain of whitish
  and often star…shaped dots; about 2 mm。 in diameter。  The
  appearance thus presented was curiously like that of a leaf; into
  which the larva of some minute insect had burrowed。  But my son
  Francis; after making and examining sections; could nowhere find
  that the cell…walls had been broken down or that the epidermis had
  been penetrated。  When the section passed through the whitish dots;
  the grains of chlorophyll were seen to be more or less discoloured;
  and some of the palisade and mesophyll cells contained nothing but
  broken down granular matter。  These effects must be attributed to
  the transudation of the secretion through the epidermis into the
  cells。
  The secretion with which worms moisten leaves likewise acts on the
  starch…granules within the cells。  My son examined some leaves of
  the ash and many of the lime; which had fallen off the trees and
  had been partly dragged into worm…burrows。  It is known that with
  fallen leaves the starch…grains are preserved in the guard…cells of
  the stomata。  Now in several cases the starch had partially or
  wholly disappeared from these cells; in the parts which had been
  moistened by the secretion; while it was still well preserved in
  the other parts of the same leaves。  Sometimes the starch was
  dissolved out of only one of the two guard…cells。  The nucleus in
  one case had disappeared; together with the starch…granules。  The
  mere burying of lime…leaves in damp earth for nine days did not
  cause the destruction of the starch…granules。  On the other hand;
  the immersion of fresh lime and cherry leaves for eighteen hours in
  artificial pancreatic fluid; led to the dissolution of the starch…
  granules in the guard…cells as well as in the other cells。
  From the secretion with which the leaves are moistened being
  alkaline; and from its acting both on the starch…granules and on
  the protoplasmic contents of the cells; we may infer that it
  resembles in nature not saliva; {22} but pancreatic secretion; and
  we know from Fredericq that a secretion of this kind is found in
  the intestines of worms。  As the