Page:Evolution of Life (Henry Cadwalader Chapman, 1873).djvu/38

30 simple and characteristic structure, and turn to the other descendants of Amoebae, as seen in Tree I.

In the alimentary canal of the earth-worm, of cockroaches, etc., are often found sac-like bodies, called Gregarinae. (Fig, 10.) These simple creatures are nearly destitute of organs, having simply in one part of their body a small nucleus and nucleolus, and a delicate muscular fibre. Nourishing itself by imbibing the juices of the animal in which it lives, slowly narrowing or lengthening its body in different directions,—this motion being probably caused by the delicate muscular fibre just mentioned,—the Gregarina passes its existence. At times, however, this motion ceasing, it takes the shape of a sac. (Fig. 10, b.) The nucleus and nucleolus disappear. The substance of the body breaks up into what have been called pseudo-navicellae, from their resemblance to the Navicula. The contents of the navicellae (Fig. 10, d) are changed under favorable circumstances into Amoeba-like bodies (Fig. 10, e, f, g, h), which, in their turn, become Gregarinae. By looking at Tree I. we see Amoebae, or their haired descendants most likely, divided into four groups:—1st, the Sponges, whose supposed progeny we have treated of as Coelenterata; 2d, Gregarinae, whose Amoeba-like development clearly indicates their ancestry, which we now leave; 3d, Infusoria, whose young show in a marked degree their affinity to the Amoebae and to the Worms; 4th, the Noctilucae, the animals (allied to the Infusoria) causing the phosphorescence of the sea by the immense numbers of them found together in tropical climates.

The animalcula of ditches and ponds are made up, in a great measure, of the microscopical beings called Infusoria