606 L- R- Cary, 



three on either side. These correspond in their relation and dis- 

 tribution to the main trunks which have been described in the adult 

 worm. In the cercaria, however, the dorsal pair of longitudinal 

 nerve trunks are by far the larg-est. The lateral and ventral trunks 

 arise later in the development of the cercaria and up to the time 

 of encystment are scarclej^ more than large nerves. 



Reproductive o l' g a n s. 



The reproductive system in the cercaria consists of well defined 

 masses of cells, which have not 3^et taken on the definite shapes of 

 the fully formed reproductive organs. The two testes, the ovar}', 

 the penis sheath, the uterus and the vitellaria can be recognized as 

 sharply marked out cell areas; but not as yet as organs of similar 

 structure to those of the adult. The testes are, in the living con- 

 dition, by far the most prominent of the reproductive primordia. 

 All of the others may be seen rather indistinctly. 



The cystogenous glands. 



In the living cercaria, the cystogenous glands appear as two 

 opaque masses, one on either side of the bod}", which extend nearly 

 its entire length. With a strong illumination the granular contents 

 of the cells can be made out very clearly. In section (Fig. 7), each 

 gland is seen to be made up of a mass of large pear-shaped cells, 

 each of which opens to the exterior by a separate duct. The in- 

 terior of each cell is almost entirely filled with large granules which 

 stain intensely with haematoxylin. The large nucleus is crowded 

 to one side of the cell, and the cytoplasm is restricted to the inter- 

 stices between the granules of the secretion. When the cj^st is 

 formed, tlie granular contents of these cells is thrown out and con- 

 verted into the cyst, while the cells shrink to a comparatively small 

 size. Fig. 8, a section through a cercaria which had given out the 

 cystogenous material while still witliin the body cavity of the redia, 

 shows the condition of the gland cells after they have become free 

 from the secretion. This section shows also the thickness of the 

 mass of secretion before it has had time to harden. 



In AmpMstomnm subdavatum, according to Loess, the material 

 from which the cyst is to be formed exists inside the gland cells in 

 the shape of "Stäbchen" which are strongly refractive and do not 

 take any stain at all. 



A comparison of Fig. 6 with Looss' (1892), fig. 20, tab. 20, will 



