26 WRIGHT AND MACALLUM. [Vol. I. 



those of Lang, except that the cytoplasma was strongly reticu- 

 lar, and when these were compared with the cells described 

 above we were inclined to think that the former were in a stage 

 of transition to the latter. When a careful study of a number 

 of both kinds of cells was made it was seen, however, that they 

 were essentially unlike. As mentioned above, the cells which 

 appear perforated give origin to the brushes of cilia found in the 

 larger excretory trunks, and, therefore, these may correspond 

 to the cells described by Lang. 



The fact that an extension of the cell in the form of a process 

 is not seen in preparations made with the chrom-osmio-acetic 

 mixture is probably due to the reagent, and partly to the sec- 

 tioning. In respect to the latter it is to be expected that a 

 unipolar cell variously placed in the tissue would be cut in 

 various planes, and that sections involving both the body of 

 the cell and the process would be rare. When the long axis 

 of the cell occurs in sections its demonstration is not distinct, 

 for the structure of the pole or neck of the cell is formed of 

 material indifferent to staining. We made experiments with 

 different reagents in order to determine which one would afford 

 the best demonstration of the presence of a pole to the cell. 

 Such a reagent we found to be Lang's fluid, which enhances the 

 staining power of cells, at the same time altering their cytologi- 

 cal structure. It so affects the cells in question that both cell 

 and nucleus stain a red tint with alum-cochineal. The polar 

 process in this case stains also, but the less so the farther from 

 the body of the cell. Observed in this way these cells are ex- 

 tremely similar in shape to unipolar ganglion-cells. They do 

 not now reveal such an internal structure as is described above, 

 the clear central space is often absent, the nucleus is large and 

 spherical, the cytoplasma gives slight or no trace of radiating 

 trabeculae, and the neck of the cell has slightly granular contents. 

 Such preparations have, however, given the clearest results as 

 to the presence of an axial channel in the polar process, and 

 as to the connection of this process with excretory vessels. This 

 connection suggests that they have a depuratory action ; that is, 

 that they are renal in the strict meaning of that term. 



To this class we also assign the cells which are found in the 

 muscular pharynx. These are in their greatest measurements 

 35 ^, and their nuclei vary in diameter between lo ^ and 20 ^. 



