15] LIFE HISTOR Y OF TREMA TODES—FA UST 15 



those cells which remain unquestionably embryonic. He distinquishes between 

 the condition in rediae and sporocysts, for in the former he found a specialized 

 germinal epithelium, while in the latter all of the cells of the body wall remain 

 undifferentiated in character, and in consequence are capable of germ cell 

 production. 



Thomas (1883:119) found for the sporocyst-redia generation of Fasciola 

 hepatica that the germ balls which develop into rediae arise in part from ger- 

 minal cells already present in the embryo (sporocyst), but that " they gain an in- 

 crease in their numbers by the proliferation of cells lining the body cavity. " 

 In the rediae he asserts (p. 125) that the majority of the embryos seem to be 

 formed from the transformation of cells at the posterior end. Cells from the body 

 wall become enlarged, and each of these cells undergoes segmentation, giving 

 rise to a morula. Looss (1892:156, 157) is definitely conmiitted to the view 

 that any portion of the epithelium Uning the body cavity is capable of produc- 

 ing germ balls, but, as a matter of fact, only the posterior end (the vegetative 

 end) performs such service. Later in the same paper (p. 167) he speaks of the 

 developmental stages as a metamorphosis composed of several generations, in 

 no sense comparable to parthenogenesis. Haswell (1903:500, 501) describes 

 for the sporocyst of an echinostome larva the development of embr^'os from a 

 single ovarian mass at the posterior end of the body. 



Within more recent years the problem of the origin of germ balls has been 

 centered around the criterion of the formation of polar bodies. Coe (1896: 

 562) found no polar bodies in the germinal epithelium of the sporocyst and 

 redia of Fasciola hepatica. Because Reuss (1903:470) found three small gran- 

 ular bodies attached to the germ balls of Distomum duplicatuni sporocysts, he 

 concluded that maturation occurred. Tennent's work on Bucephalus haimae- 

 nus (1906:649) supports the argument in favor of the origin of the germ cell 

 from the walls of the body cavity. After the germ cell passes into the body 

 cavity a "polar body" is cut off. Later Tennent has found that there are 

 three cells in the proximity of the germ cell, two of which seem to be the result 

 of division of the first cell. Rossbach (1906:433) finds no cells which he is 

 willing to call polar bodies. He concludes 1) that the small cells near the epithe- 

 lium are not polar bodies because their walls are not found in direct continuity 

 with the germ cells; 2) that the cells called polar bodies by Reuss are normally 

 present during development of the germ ball, in miracidia, in sporocysts, in 

 rediae, and even in the ovary of sexually mature trematodes; 3) that they are 

 more abundant in the younger sporocysts and rediae, and 4) that they are pre- 

 sent in larger nimabers than three's. Finally Gary (1909), in his study of the 

 germ cells of an amphistome sporocyst, has found that the germ balls arise 

 from cells of the body wall which mature without reduction and throw o£E 

 one polar body. 



The contribution to the problem of the meaning of the proliferation of germ 

 balls as described in this paper, is based on the development of the germ cells 

 in the rediae of the holostome, Cercaria flabelliformis Faust 1917. In the 



