These spores were taken into the intestine with other food; they penetrated the thin wall of the intestine, passed into the body cavity, multiplied there, and in consequence the animal died.

In many cases, however, those penetrating became enclosed in cells which the body cavity contains and which correspond with the leucocytes of the blood; in these the spores were digested and destroyed.

The daphneae in which this took place recovered from the infection.

Here was a case in which all the stages of an infectious disease could be directly followed under the microscope, and the whole process was simple in comparison with infections in the higher animals.

The pathogenic organism was known, the manner and site of invasion was clear, it was also evident that if the multiplication of the parasite was unchecked the animal died, but if the parasite was opposed by the body cells and destroyed the animal recovered.