Small wonder that scientists were in doubt concerning the true nature of _Euglena_, its non-walled cell and peculiar mode of feeding are indeed puzzling. There are many similar cases amongst these lowly organisms, in fact there are some creatures which may best be described as partly plant and partly animal. Those of our readers who are interested in such problems may read an excellent account given much more fully than we could give it here, in Professor F. W. Keeble’s _Plant Animals_, one of the excellent Cambridge Manuals of Science. The fact is that the demarcation between plants and animals, low in the scale of development, is not nearly so pronounced as it is amongst the higher forms of life. Amongst the plants of our pond we shall find that, like the land plants, most of them are green, and many of them are thread-like, so that the task of distinguishing one from another may appear difficult. Examined with the naked eye, many of them appear remarkably similar to one another; under the microscope the differences are obvious. One of the most remarkable of the commoner pond plants is known as _Oscillatoria_; it does not boast of a popular name but its scientific name is not very difficult to remember after we have witnessed its oscillations. _Oscillatoria_ is a plant with particularly animal-like movements. It is merely a thread, usually green-blue in colour, but sometimes red or violet. The threads are never branched and, except when in motion, are straight. Under a moderately high magnification we can see that this thread-like plant is not composed of a single cell but that it consists of a number of cells, placed end to end. Sometimes a few of these cells will break away and start life on their own account. Whatever interest the structure of _Oscillatoria_ may have for us, we cannot help being struck with its movements, and we must make a point of observing them. The movement is peculiar and not easy to describe nor, so far as we know, has it ever been explained. A thread will be seen to glide backwards and forwards, becoming somewhat curved and, at the same time, revolving on its axis. Eel-like is perhaps a good description of the movement. It is possible to distinguish this plant from other pond dwellers by its slimy “feel” which arises from the fact that each thread is enclosed in a jelly-like sheath.