The Common Liver Entozoon of Cattle. 121 



6. The freed eggs, if mature, contain ciliated embryos, 

 capable of active progression when brought in contact with dew 

 on the blades of grass, rain-drops, pools of water, ponds, and 

 lakes. The prolonged action of moisture without, aided by 

 vigorous movements of the perfected embryo within, serves to 

 loosen the lid-like end of the egg-shell, by the opening of 

 which the animalcule is set free. 



7. The ciliated embryo, or proscolex, as Van Beneden calls 

 it, contains within itself a solitary germ, which is developed by 

 a process of internal budding into a non-ciliated larva, or 

 scolex in the language of the Louvain Professor. 



8. The ciliated embryo, after swimming about for a time, 

 sooner or later selects and attaches itself to the surface of the 

 body of a pond-snail, a slug, or the soft body of some aquatic 

 insect. In this situation it looses its ciliated covering, and 

 subsequently gains access to the interior of the selected host. 



9. Once within the viscera of its host, the embryo disap- 

 pears, leaving the hitherto contained germ-bud, or scolex, to 

 undergo its further development, which is accomplished rapidly, 

 a second progeny being at the same time formed within its 

 own interior. 



10. The enlarged and independent scolex is now trans- 

 formed into a large sac, or cyst, for the support and protection 

 of its contained progeny. In this condition it is frequently 

 called a " Nurse/ 7 or " Sporocyst," and when rather highly 

 organized, is known by the title of ' ' Redia/' 



11. The nurse-progeny, or trematode larvse, thus produced 

 within the scolex, are usually furnished with tails, and when 

 fully developed are the well-known Cercari.33. Yan Beneden 

 calls them proglottides, but the term is inappropriate. 



12. The Cercarias have a tendency to migrate from the 

 bodies of their molluscan or insect hosts, and they are quite 

 capable of an independent existence. During these wanderings 

 in the water, or in moist pastures, they are occasionally brought 

 in contact with the human body, and, in a few instances, ap- 

 pear to have succeeded in penetrating the skin. 



13. It is not certain whether the Cercarise are taken into 

 the bodies of quadrupeds when the latter are drinking water 

 or eating solid food, but it is probable that they are trans- 

 ferred in either way. It is not unlikely that they are often 

 swallowed while still within the bodies of their molluscan or 

 insect hosts. 



14. From the digestive organs of the sheep or cattle the 

 Cercarise bore their way through the tissues into the liver, in 

 which situation they part with their tails, and become encysted. 

 This constitutes the so-called jpupa stage. 



15. The pupa, thus encysted for many weeks, or even 



