I will now give you the facts in relation to two which shall be typical.  We obtained them in enormous abundance in a maceration of fish.  I will not take them in the order of our researches, but shall find it best to examine the largest and the smallest.  The appearance of the former is now before you.  It is divergent from the common type when seen in its perfect condition, avoiding the oval form, but it resumes it in metamorphosis.  It is comparatively huge in its proportions, its average extreme length being the 1/1000 of an inch.  Its normal form is rigidly adhered to as that of a rotifer or a crustacean.  Its body-substance is a structureless sarcode.  Its differentiations are a nucleus-like body, not common to the monads; generally a pair of dilating vacuoles, which open and close, like the human eyelid, ten to twenty times in every minute; and lastly, the usual number of four flagella.  That the power of motion in these forms and in the Bacteria is dependent upon these flagella I believe there can be no reasonable doubt.  In the monads, the versatility, rapidity, and power of movement are always correlated with the number of these.  The one before us could sweep across the field with majestic slowness, or dart with lightning swiftness and a swallow’s grace.  It could gyrate in a spiral, or spin on its axis in a rectilinear path like a rifled bullet.  It could dart up or down, and begin, arrest, or change its motion with a grace and power which at once astonish and entrance.  Fixing on one of these monads then, we followed it doggedly by a never-ceasing movement of a “mechanical stage,” never for an instant losing it through all its wanderings and gyrations; We found that in the course of minutes, or of hours, the sharpness of its outline slowly vanish, its vacuoles disappeared, and it lost its sharp caudal extremity, and was sluggishly amoeboid.  This condition tensified, the amoeboid action quickened as here depicted, the agility of motion ceased, the nucleus body became strongly developed, and the whole sarcode was in a state of vivid and glittering action.

If now it be sharply and specially looked for, it will be seen that the root of the flagella splits, dividing henceforth into two separate pairs.  At the same moment a motion is set up which pulls the divided pairs asunder, making the interval of sarcode to grow constantly greater between them.  During this time the nuclear body has commenced and continued a process of self-division; from this moment the organism grows rapidly rounder, the flagella swiftly diverge.  A bean-like form is taken; the nucleus divides, and a constriction is suddenly developed; this deepens; the opposite position of the flagella ensues, the nearly divided forms now vigorously pull in opposite directions, the constriction is thus deepened and the tail formed.  The fiber of sarcode, to which the constricted part has by tension been reduced, now snaps, and two organisms go free.  It will have struck you that the new