124 A. P. THOMAS. 



duals, but also according to the amount of food contained in 

 it. It reaches its full size early ; indeed, in a redia not half 

 grown it may be as long as in a full-grown example. 



The body-cavity is traversed in different directions by bridges 

 or trabeculse of tissue, in which cells of various shapes, some of 

 them with long processes, can be distinguished. This tissue is 

 most abundant in the anterior part of the redia around the 

 pharynx and digestive tract, and here often contains fibres, 

 probably contractile. Its amount varies very greatly in differ- 

 ent specimens, and behind the digestive tract is sometimes alto- 

 gether absent. At other times it is so extensively developed 

 that the cavity of the redia appears to be divided up into a 

 number of imperfect compartments, in which the germs lie 

 loosely. De Filippi appears to have observed similar trabeculse 

 in the redia of Cercaria coronata, of which he says,^ " La 

 cavite du corps est traversee sans ordre par des brides." 



There is always a good deal of tissue around the pharynx 

 and beginning of the digestive tract, and embedded in it may 

 be seen, in favorable specimens, a few large round cells witli 

 clear protoplasm and large nucleus; each has a process or 

 duct (?) passing towards the angle formed by the junction of 

 the digestive sac with the pharynx. They are probably glan- 

 dular in function. At the side of the redia, a little behind the 

 collar, there is present a birth-opening (PI. Ill, fig. 13, v), which 

 permits the exit of the brood when ready to leave the parent. 

 Such an opening has been seen in a number of redise of different 

 types, and probably exists in all. 



The germs produced within the redia develop either into 

 daughter-redise or into cercarise, and it appears to me that slight 

 differences exist between the individuals giving rise to one or the 

 other of these generations. A redia producing redijE is usually 

 smaller, but its pharynx and digestive sac are larger ; for ex- 

 ample, two rediae were taken from the same snail, one producing 

 redise measured less than 1 mm. long, with a pharynx '117 mm. 

 and an intestine '41< mm. in length, whereas in the slightly larger 

 redia containing cercarise the pharynx measured '078 mm. and 

 ' Ibid., vol. xvi, p. 426. 



