10 BULLETIN OF THE 



ditions. Besides the striations in the cells, there appear creases or folds 

 resulting from the pressure of the rhabditi. 



In thick sections through regions where the rhabditi are numerous, 

 the epidermal cells have the appearance of being joined to the basement 

 membrane by foot-like processes. This appearance at first led me to 

 believe in a condition like that described by Iijima, and it was only 

 after studying sections of material in which the rhabditi had been 

 removed (Fig. 3) that I understood their relations to the cells. 



The rhabditi do not lie in the hypodermal cells, but between them. 

 Kennel ('79, p. 126) and Braun ('81, p. 305) are the only observers who 

 have described them as having an intercellular position. It will be seen 

 from the following description of their development in Phagocata, that 

 such a position is the only natural one. The presence of these rods 

 between the cells produces a crowding, and the pressure is so great that 

 it causes the cells to become displaced and much modified in shape. 

 The nuclei may be pushed out to the free ends of the cells, or crowded 

 down to their bases, and the cells themselves may be so reduced as to 

 appear like mere filaments (Fig. 3). Kennel ('79, p. 126) describes' the 

 epidermal cells of Rhynchodesmus after the removal of the rhabditi, as 

 "feine Fadcheu ... so lang als die Epidermis dick ist." Regarding 

 their intercellular position, Braun ('81, p. 305) states for Bothrioplana 

 that the rhabditi "nicht allein zwischen den Zellen stehen, sondern auch 

 das Protoplasma der Zellen durchbohren." In Phagocata, as in Rhyn- 

 chodesmus, the rhabditi are so numerous that the hypodermis appears at 

 first to be entirely composed of them. As Kennel expresses it, " ausser 

 den feinen, fadenformigen Zellen kaum etwas anderes Platz zwischen 

 ihnen hat." It is in thick sections, where the epidermis is many layers 

 deep, that the bases of these compressed cells present an appearance as 

 if the hypodermis were connected with the basement membrane by fine 

 foot-like processes. This appearance is only seen where the rhabditi are 

 most numerous. At the lateral edges of the body, where there are few, 

 and where consequently the cells retain their primitive cylindrical form 

 (Fig. 2), the latter are applied to the membrane by their broad bases. 

 It is in these regions also that the striations previously spoken of are 

 most distinctly seen. 



Moseley ('74, p. 118) says, "The epidermis here [land planariansj is 

 seen to be made up of large gland-cells and cells containing rod-like 

 bodies and a certain amount of vertical filaments." "The irregular fila- 

 ments which fill up the interspaces between the gland-cells and rod-like 

 bodies appear to be the remains of the cell-walls and rod-like bodies." 



