are growing together they appear like a delicate growth of mold upon the water weed. The stalk is peculiar in being traversed by a muscle fiber arranged in a loose spiral, which, upon any unusual disturbance, contracts together with the body into the form shown in Fig. 10, b.

These few examples serve to show the general plan of organization and the method of locomotion of the Infusoria; but, as upward of a thousand species exist, with widely differing habits, many interesting modifications are present. Some have been driven in past time to adopt a parasitic mode of life within the bodies of other animals. At present they are devoid of locomotor organs, and as they absorb nutritive fluids through the surface of the body all traces of a mouth are also absent. The reproductive processes also are peculiar, but they do not concern us now.

29. Gregarina. Another type of protozoan worthy of special attention is that of the Gregarina (Fig. 11), various species of which live in the alimentary canal * of crayfishes and centipeds and certain insects. Gregarina is a parasite,

living at the expense of the host in whose body it lies. It has no need to swim about quickly, and hence has no swimming cilia like Paramecium and the young Vorticella. It does need to cling to the inner wall of the alimentary canal of its host, and the body of some species is provided with hooks for that purpose. The food of Gregarina is the liquid food of the host as it exists. in the intestine, and which is simply absorbed anywhere through the surface of the body of the parasite. There is no mouth opening nor

*Specimens of Gregarina can be abundantly found in the alimentary canal of meal worms, the larvæ of the black beetle (Tenebrio molitor), common in granaries, mills, and brans. "Snip off with small scissors both ends of a larva, seize the protruding (white) intestine with forceps, draw it out, and tease a portion in normal salt solution (water will do) on a slide. Cover, find with the low power (minute, oblong, transparent bodies), and study with any higher objective to suit."MURBACH.

fixed point of ejection of waste material, nor is there any contractile vacuole in the body.

In the method of multiplication or reproduction Gregarina shows an interesting difference from Amaba and Paramecium and Vorticella. When the Gregarina is

FIG. 11.-Gregarinidæ. A, a Gregarinid (Actinocephalus oligacanthus) from the intestine of an insect (after STEIN); B and C, spore forming by a Gregarinid (Coccidium oviforme) from the liver of a guinea-pig (after LEUCKART); D, E, and F, successive stages in the conjugation and spore forming of Gregarina polymorpha (after KOELLIKER).

ready to multiply, its body, which in most species is rather elongate and flattened, contracts into a ball-shaped mass and becomes encysted-that is, becomes inclosed in a tough, membranous coat. This may in turn be covered externally by a jelly-like substance. The nucleus and the protoplasm of the body inside of the coat now divide into many small parts called spores, each spore consisting of a bit of the cytoplasm inclosing a small part of the original nucleus. Later, the tough outer wall of the cyst breaks, and the spores fall out, each to grow and develop into a new Gre

garina. In some species there are fine ducts or canals leading from the center of the cyst through the wall to the outside, and through these canals the spores issue. Sometimes two Gregarina come together before encystation and become inclosed in a common wall, the two thus forming a single cyst. This is a kind of conjugation. In some species each of the young or new Gregarinæ coming from the spores immediately divides by fission to form two individuals.

Related to the Gregarina are those minute protozoan parasites which live in the blood-corpuscles of man and some of the lower animals, and are called Hæmatozoa. Three species of these, living in the blood of man, cause the three kinds of malarial fever, known as tertian, quartan, and remittent. These malarial Hæmatozoa, .known generally as Hamamæba, can multiply by asexual sporulation in the blood, but produce also certain sexual individuals, which, when taken into the stomach of a mosquito which has sucked blood from a malarial patient, give rise to a zygote which encysts in the outer walls of the stomach, and breaks up into numerous blasts or embryos, which escape into the blood of the mosquito, and thence to all parts of its body, and especially to the salivary or poison glands. When now this infected mosquito pierces the skin of another man, and pours into the wound, as it regularly does, a quantity of saliva, numbers of larval Hamamabæ also enter the blood, and, multiplying here, soon set up the disease malaria in the bitten person. It has been definitely proved that malaria is thus disseminated by mosquitoes, and it is highly probable that it is contracted in no other way.

30. Characteristics common to the Protozoa. We have now studied the principal structures which serve in locomotion among these simple one-celled forms, also the means by which they catch their food, and we shall now glance at the internal processes, which are much the same in all.

After the food has been taken into the cell, it is proba

bly acted upon by some digestive fluid, for it soon assumes a granular appearance, and finally undergoes complete solution. In every case the oxygen is absorbed through the general surface of the body, and uniting with the living substance, as in the squirrel, liberates the energy necessary for the performance of the animal's life-work. The wastes. thus produced in a large number of forms simply filter out from the body without the agency of anything comparable to a kidney, but in several species they are borne to a definite spot, the pulsating vacuole (Figs. 7, 9, 10, c.v.), where they gradually accumulate into a drop about the size of the nucleus. The wall between it and the exterior now gives way, and the excretions are passed out. In active individuals this process may be repeated two or three times a minute, but it is usually of less frequent occurrence.

The loss in bodily waste is continually made good by the manufacture of the food into protoplasm, and if the income be greater than the outgo, growth ensues. But, as in all other forms, growth is limited, and ultimately the cell is destined to divide, resulting in two new individuals. This process may be repeated many times, but not indefinitely, for sooner or later various members of the same species unite in pairs temporarily or permanently, exchange nuclear material, and separate again with apparently renewed energy and the ability to divide for many generations.

31. Simple and complex animals.—It is important to note that these same processes of waste, repair, growth, feeling, motion, and multiplication are the same as those of the squirrel, and, furthermore, are common to all living creatures, so that the difference between animals is not in their activities, but in their bodily mechanisms; and according to the perfection of this, the animal is high or low in the scale. Comparing, for example, the Amaba and Slipper Animalcule, which are relatively low and high Protozoa, we find in the former that any part of the body serves in locomotion and in the capture of food, while in the latter these

same functions are performed by definite structures, the cilia and gullet. Now, it is well known that a workman is able to make better watch-springs, when this is his sole duty, than another who must make all parts of the watch; and likewise, where a definite task is performed by a definite structure, it is more efficiently done than where any and every part of the body must carry it on. So the Amaba, in which definite tasks are performed by any part of the body indifferently, is less perfect and thus lower than the Paramecium, where these functions are performed by special organs. As we ascend the scale of life we find this division of labor among special parts of the body more complete, the organs, and therefore the animal, more complex, and better fitted to carry on the work of its life.