110 BRUCE D. REYNOLDS. 



METHODS. 

 (a) Apparatus and Technique. 



In carrying out these experiments more standardized and exact 

 methods were employed than those used in the first article of this 

 series, though they were essentially the same. In every case 

 (unless specified) distilled water (pH -- 0.7) was used, and each 

 animal was washed once or twice before being transferred to the 

 slide on which the amputations were made. Furthermore, any 

 detritus clinging to the shell was removed before the operation. 

 In all of the cross-fusion experiments the two organisms to be 

 tested were placed on the same slide, and when a fragment was 

 severed from one, that individual was moved away and the other 

 placed near the fragment of protoplasm. The glass needles, 

 with which the protoplasmic masses were detached, were drawn 

 from standard Pyrex tubing \ OD furnished by the Corning Glass 

 Company, Corning, N. Y. All operations were performed under 

 the compound microscope 32 mm. objective and No. 10 eye- 

 piece (B. & L.) while the 16 mm. objective was used in making 

 the observations. A camera lucida was attached to the micro- 

 scope and at intervals (usually one minute) the outlines of the 

 objects were traced with a pencil. These sketches were 170 

 times the size of the objects. 



The pseudopods of A. polypora are usually digitate and rarely 

 extend far beyond the periphery of the shell, making it very 

 difficult to sever masses of protopiasm by cutting. them off with a 

 needle as was done in the case of Difflugia. This difficulty was 

 overcome by taking advantage of two things (a) the shape of 

 the shell, and (b) the fact that if undisturbed for a while the 

 animal ordinarily attaches itself to the substratum. The or- 

 ganism is shaped somewhat like a shallow bowl, the outer rim of 

 the shell forming a rather sharp edge, Fig. 2. If, after a pseudo- 

 pod has been extended beyond the outer margin, pressure is 

 applied to the top of the shell the pseudopocl will be caught be- 

 tween the rim and the sub-stratum and its distal end will thus be 

 pinched off. Severance is aided by the animal's sudden reaction 

 to this stimulus. Sometimes a specimen would fail to protrude 

 pseudopods of sufficient length to permit use of the method just 

 described; consequently it was left undisturbed for a few min- 



