closest approximation, the outline has a subcircular figure. It is on account of this change of form that I presume the masses themselves to be partially composed of muscle." These remarks, although specially made of the _Rotifer macrurus_, are in the main applicable to all the Philodinas, but the student must not expect to understand any of the complicated gizzards of the rotifers without repeated observations, and no small exercise of patience. It is common to call the portions of the Philodine-pattern gizzard "stirrup-shaped," but Mr. Gosse has shown them to be _quadrantic_, that is, shaped like the quarter of a sphere. As we are not very well off with subjects for description in these two months, we can afford a little time to consider a question that continually arises in the mind, on viewing the movements of animalcules, and especially of any so highly developed as the rotifers, namely, to what extent motions which appear intelligent are really the result of anything like a conscious purpose or will. When any of the lower animals--a bee, for example--acts in precisely the same way as all bees have acted since their proceedings have been observed, we settle the question by the use of the term _instinct_. Those who take the lowest view of insect life, assume that the bee flies because it has wings, but without wishing to use them, and that the nerves exciting them to action are in their turn excited, not by volition, but by some physical stimulus. The sight or the smell of flowers is thought by the same reasoners to be capable of attracting the insect, which is unconscious of the attraction, while proximity of food stimulates the tongue to make the movements needful for its acquisition, and so forth. The cells, they tell us, are built according to a pattern which the earliest bee was impelled to construct by forces that bear no analogy to human reason and human will, and so originate all the ordinary processes of bee life. Sometimes, however, it happens that man or accident interposes particular obstacles, and forthwith there appears a particular modification of the orthodox plan, calculated to meet the special difficulty. How is this? Does any one of the difficulties which the bee or the ant is able to get over, produce precisely that kind of electrical disturbance, or polar arrangement of nerve particles that is necessary to stimulate the _first_ step of the action by which the difficulty is surmounted; and does the new condition thus established stimulate the _second_ step, and so forth, or can the bee, within certain limits, really _think_, design, and contrive?