1922] Rees: The Neuromotor Apparatus of Paramaecium 337 



which was dropped on the slide while hot. The same processes of 

 staining were employed as were used by Sharp (1917) and Yocom 

 (1918). The system appears as a network of fine anastomosing 

 fibrils in the ectoplasm. 



Another method of staining with Mallory's was as follows: The 

 organisms were killed and fixed either in Zenker's fluid or piero- 

 mercuric (Yocom, 1918) sohition in centrifuge tubes. They were 

 placed by means of a pipette in a small piece of folded silk bolting 

 cloth. In this they were run through the stains and alcohols to 

 xylol, then transferred to a Lefevre watch glass and concentrated in 

 the groove by means of a camel's hair brush. A drop of balsam was 

 added and they were placed on the slide by means of a pipette. The 

 surface fibrils did not show in animals so stained, but clear views of 

 the eytostomal and cytopharyngeal systems were obtained. 



Iron alum haematoxylin was by far the best stain. Schaudinn's 

 solution used hot was the best fixer. The animals nearly always dis- 

 charged their trichocysts. Picro-mercuric used hot sometimes fixed 

 the animals with trichocysts intact, biit they did not stain so well as 

 when Schaudinn's fluid was used. The fact that trichocysts are dis- 

 charged in Schaudinn's is fortunate for whole mounts, as otherwi.se 

 the dorsal and ventral whorls of fibrils would not be made visible. In 

 only four of over twenty trials was success attained with whole 

 mounts, the difficult part of the process being the destaining, which 

 required from two to four hours with cold 2 per cent iron alum. 

 Sometimes the animals turned yellow or became opaque and had to 

 be discarded. When destaining goes on as is desired, the organisms 

 change color from black to blue and then to bluish gray, and the 

 protoplasm is always quite clear. The end of the destaining process 

 is reached when they are quite gray with the nucleus still quite dark. 

 Only faint outlines of the neuromotor system can be seen at this 

 time even with oil immersion. The whorls of ramifying fibrils become 

 clearly differentiated only after clearing in xylol and balsam. 



Infiltration and imbedding were carried out at first in gelatine 

 capsules as described by Metcalf (1908), but later it was found that 

 glass capsules made of tubing by sealing one end in the flame were 

 more satisfactory. 



As will be shown by an examination of the plates, the thick sec- 

 tions (15/j.) were very valuable because they gave more extensive 

 views of the cytopharyngeal fibers than did the thin ones. The lines 

 of basal granules and trichocysts were most clearly seen in unstained 



