64 DEVELOPMENT OP 



like a broad fringe surrounding the body, and frequently 

 appears as if it were folded, and consisted of two laminae. 

 At some distance posterior to the middle of the body are 

 situated the two characteristic oblique processes, and 

 which, as well as the part of the trunk posterior to them, 

 which I designate a tail, are simply local dilatations of 

 the cavity of the body. Of internal organs there is only 

 to be seen an undivided sacculated stomach, very small in 

 proportion to the size of the animal, and into which the 

 oesophagus opens, (see fig. 4 (5.) The whole remainder of 

 the very large body is filled with the brood of Cercarice. 

 In the instance figured at 4 h, all the embryos have 

 simultaneously attained their full development, which is 

 but very seldom the case, since, in the same individual, 

 Cercarice are found in all stages of development. 



The whole series of forms which the Cercarice pass 

 through within the body of their foster-parent, is repre- 

 sented in (fig. 5 a — 5 m.) hi first the germs from which 

 the Cercarice are developed are nearly spherical, and 

 appear to be formed of numerous vesicular globules or 

 cells, which are pretty clearly seen to be all surrounded 

 by a very delicate common membrane. These spherical 

 germs afterwards increase in length as they are formed 

 into embryos, and during this growth one end becomes 

 much more dilated than the other. This unequal deve- 

 lopment continues in two opposite directions, so that the 

 more slender end gradually forms the tail of the embryo, 

 and the thicker its body. Thus the body and tail are at 

 first not merely united very closely, but form externally 

 one whole, and so long as this is the case, very weak mo- 

 tions are observed in the embryo, for instance, when it is 

 irritated by any foreign matter, such as acids, &c., but it 

 is not entirely inanimate. As its growth continues, the 

 embryo begins to wriggle about with a worm-like motion, 

 and the more slender portion shows externally a dispo- 

 sition to separate itself from the thicker part ; but no very 

 lively motion is observable until the depression between 

 the tail and head is so marked, that the former can be 



