204 ANNIE PORTER. 



resembles that of the pre-flagellate stages, for before it is 

 accomplished the flagella have almost disappeared. Some- 

 times no flagellum is visible at all, and the parasites look 

 like dividing cysts. 



On rare occasions the posterior end of a flagellate has 

 divided before the anterior end (PI. 13, fig. 98j. 



The Hereditary Infection of Melophagus ovinus by 

 Crithidia melophagia. 



Casnal infection of Melophagus ovinus by the ingestion 

 of post-flagellate cysts of Crithidia melophagia is fairly 

 easily observed. The development of the parasite in the egg 

 can only be studied with difficulty. I now wish to give a 

 fuller account than exists up to the present of the processes 

 leading up to the birth of Melophagus infected with 

 Crithidia melophagia. 



The first point to be determined was the way in which the 

 Crithidia reached the egg. Infected Melophagus were 

 carefully dissected so that no rupture of the gut was made. 

 The ovaries also were dissected out and kept as far as 

 possible in the position beside the gut that they occupied in 

 life. Critliidia could be seen through the gut- wall moving 

 actively about. Suddenly they concentrated in one place 

 and soon began to pass through the wall, their posterior 

 (blunt) end first. They rapidly swam direct to the ovaries 

 and penetrated them in the same way, that is, with the non- 

 flagellar end first. The flagellum was very rarely used as a 

 boring organ to allow of the passage of the oi'ganism. 



Penetration of the ovaries of their host by the parasites 

 occurs in other cases, e.g. C. gerridis, H. jaculum, but 

 the ova are apparently unattacked and the flagellates simply 

 degenerate. But in the case of C. melophagia the organisms 

 (PI. 13, figs. 57, 59) make their way rapidly to the ova, to 

 which they cling, whether the ova are mature or immature. 

 In some cases one Crithidia only enters the egg (PI. 13, 

 fig. 58) ; at other times several penetrate it at once. In 



