ERNEST CARROLL FAUST. 



of a single pair of tubules. Fusion of these two canals occurs at 

 an early stage in the region of the bladder and anterior part of 

 the tail. When the pigmentation of the eye-spots first becomes 

 conspicuous three groups of flame cells are already present, each 

 group being represented by a single cell (Fig. i). Later, when 

 the animal assumes a more characteristic shape (Fig. 2), the 

 posteriormost cell and tip of the tubule has bifurcated. With 

 the maturing of the cercaria successive stages of division of the 

 anteriormost flame cell into two, four and eight cells may be 

 found. The middle cell remains single, which fact accounts for 



3 4 



FIG. 3. Mature Cercaria convoluta, with 25 flame cells on each side of the body. 



X 175- 

 FIG. 4. Excretory system in the parthenita of C. convoluta. X i?5- 



its disproportionately large size. In the posteriormost group 

 the main canal of the inner (anterior) tubule approaches its 

 mate of the opposite side and fuses with it. The cell becomes 

 oriented laterally and gives rise to eight cells. In like manner 

 the outer (posterior) tubule produces eight flame cells near its 

 median margin. Thus there are formed (Fig. 3) twenty-five 

 flame cells on each side of the body of the mature Cercaria 

 convoluta from three original groups of one flame cell each. 



