THE PHYSIOLOGY OF EXCRETION. 



99 



This central mass of vacuoles gives origin to one continuous 

 central canal, which runs through the whole length of the fol- 

 lowing cells and opens into the terminal vesicle. The same is 



FIG. 10. 



the case with the large central vacuoles which I have mentioned 

 as occurring in other species. 



The peripheral vacuoles in the next cells flow together (vc) 

 and communicate with the central canal (Fig. u). These side 

 canals finally assume the form of bushes or trees, in which 

 the stem represents the canal of communication with the cen- 

 tral canal, from which stem are 

 given off finer and finer branches 

 to the periphery of the cells 

 <Fig. 12, c). 



As soon as the central canal is 

 formed we notice new organs in 

 these cells. All along the peri- 

 phery we see, projecting into the 

 interior of the cell, coarse short 

 threads (staining deep red with 

 Bordeaux red), each thread end- 

 ing in a coarse knob, which stains 

 intensely blue with haematoxylin 

 (Fig. I3,/). The cell certainly is in a state of great activity, 

 as is also shown by continual changes taking place within the 

 nucleus. Figs. 14-19 show us nuclei as I have observed them 

 in the upper part of the nephridium. Fig. 14 shows the chro- 



FlG. II. 



