LIFE HISTORY OF THE LIVER-FLUKE. 125 



the digestive sac '24 mm. A further distinction lies in the number 

 of the progeny ; a mother-redia may contain from one to three 

 well-formed daughter rediae with a few germs in various stages 

 of growth; the highest total observed was ten. On the other 

 hand, in a well-grown redia producing cercarise, I have counted 

 a total of twenty-three. 



The early stages in the development of the spores is the 

 same, whether they are destined to become redise or cercariae. 

 Some of them may be formed from the cells which fill the body- 

 cavity in the very young rediae, but the majority seem to be 

 formed in the following wayc^Some of the cells lining the 

 body-cavity of the parent, especially those at the posterior end, 

 are greatly enlarged, and each of these germinal cells undergoes 

 segmentation, giving rise to a morula. Fig. 18 represents a 

 large number of germinal cells in the hind end of a young redia, 

 in which no morulas were yet present. Similar cells may be 

 found in the mature rediae (fig. 13 k'), for they retain the 

 power of producing more spores as the older ones reach their 

 full development and quit the parent. Hence we find in the 

 adult redia germs in all the successive stages of growth. Each 

 morula or germ is enclosed by a delicate membrane forming a 

 loose envelope. The germs are usually detached from the body- 

 wall whilst still small and lie free in the cavity of the parent, 

 but occasionally they may remain in situ in the body-wall 

 until they have attained a considerable size (fig. 13 iv'). The 

 morula soon becomes flattened on one side (fig. 12 s), and the 

 cells of this area are then invaginated, giving rise to a gastrula 

 (fig. 12 m), whilst the germ again becomes round. The oppo- 

 site sides of the archenteron are in contact, so that there is 

 rarely any archenteric cavity, and as growth proceeds and the 

 cells become more numerous it is no longer possible to distin- 

 guish the cells of the endoderm, for the cells have the same 

 size and appearance. Nevertheless it appears to me probable 

 that the cells invaginated form the digestive tract, which 

 becomes visible at a later period in the development, rather than 

 any other cells in the germ. As the germ continues to increase 

 in size the surface becomes smooth and the outline oval. 



