xxv.] CORN MILDEW AND BARBERRY BLIGHT. 187 



this fact ; but to compare the facts belonging to the 

 animals with those belonging to the plants is a case of 

 mistaken analogy, for the facts do not correspond. 



In the first place, the test experiments with Entozoa 

 have invariably been made with host animals that were 

 perfectly well known to be quite free from entozoic parasites. 

 Measures have always been taken to make this fact certain 

 before the experiments were commenced. The two series of 

 animals have in no single instance been notoriously infested 

 with parasites before the experiments were entered upon. 



The comparison that has been made between the 

 change of host in the Entozoa, and the supposed similar 

 change of host in the two parasitic fungi of spring and 

 summer mildew of corn, brings us to what we think may 

 prove a fatal objection to the connection of Puccinia with 

 ^Ecidium, and one that strikes at the root of the whole 

 hypothesis. In the entozoic animals referred to, one form 

 of the parasite, say of the liver-fluke of sheep, is sexually 

 mature in a certain mammal. These sexual individuals, 

 which produce thousands of eggs, escape by the alimentary 

 canal of the invaded animal. The eggs are dispersed by 

 wind, rain, insects, feet of cattle, and other means, and so 

 at length find their way into pools, ponds, and streams. 

 The mature eggs contain ciliated embryos, which are set 

 free on moist surfaces or in water. Each embryo contains 

 a bud which at length becomes a larva. The ciliated 

 embryo attaches itself to a second host, such as a snail, 

 slug, or aquatic insect, and so gains access to the interior 

 of the new host. In this position it becomes a non-sexual 

 larva, and capable of producing a progeny, or other larvae, 

 within itself. These secondary larvse migrate from the 

 bodies of the water insects or molluscs and become free ; 

 they are then swallowed by mammals whilst eating or 

 drinking. The larvae now bore through the tissues of the 

 new host, and enter into a pupa stage whilst within the 

 mammal, and there at length become sexually mature 

 egg-producers, and so the life, cycle becomes complete. 



