Let us note, in conclusion, that it is through the blood-system, ramifying to all parts of the body, and the nerve-system, the ramifications of which are not less perfect, that one of the larger and higher animals is knit together into an organic whole. The former carries to the cell the raw materials for the elaboration of its explosive products, and, after the explosions, carries off the waste products which result therefrom. The nerve-fibres carry the stimuli by which the explosive is fired, while the central nervous system organizes, co-ordinates, and controls the explosions, and initiates the elaboration of the explosive compounds. Blood and nerves co-operate to render corporate behaviour possible. IV.--THE BEHAVIOUR OF PLANTS A short parenthetic section on the behaviour of plants may serve further to illustrate the nature of organic behaviour. We have seen that Paramecium is apparently attracted by faintly acid solutions, and have briefly considered Dr. Jennings’s interpretation of the facts disclosed by careful observation. In the ferns the female element, or ovum, is contained in a minute flask-shaped structure (archegonium), in the neck and mouth of which mucilaginous matter, with a slightly acid reaction, is developed; and this is said to exercise an attractive influence on the freely swimming ciliated male elements, or spermatozoids, which are necessary for fertilization. “Now, it has been shown by experiment that the spermatozoids of ferns are attracted by certain chemical substances, and especially by malic acid. If artificial archegonia are prepared (consisting of tiny capillary glass-tubes) and filled with mucilage to which a small quantity of this acid has been added, they are found, when placed in water containing fern-spermatozoids, to exercise the same attraction upon them which the real archegonia exercise in nature. The malic acid gradually diffuses out into the water, and the spermatozoids are influenced by it, so that they move in the direction in which the substance is more concentrated, _i.e._ towards the tube. Although it cannot be proved that the archegonia themselves contain malic acid, as they are too small for a recognizable quantity to be obtained from them, yet there can be little doubt that the natural archegonia owe their attractive influence to the same chemical agent which has proved efficacious in experiment.”[5] In the light of Dr. Jennings’s observations, it is perhaps not improbable that this so-called attractive influence is similar to that seen in Paramecium; and that the spermatozoids enter the organic acid in the course of their random movements, and there remain. Be that as it may, the male elements collect in the mucilaginous mass, and pass down the neck of the flask until one reaches and coalesces with the female element, or ovum, and effects its fertilization. Here we have organic behaviour unmistakably directed to a biological end--behaviour which may indeed be accompanied by some dim