REACTIONS OF CELL-BODIES OF DIFFLUGIA. 33 



nata, D. corona, D. pyriformis, D. spiralis, and D. vulgaris. 

 While only two or three observations were made on each combina- 

 tion, the results were all negative. Therefore, we feel a degree of 

 assurance in asserting that cross- fusions do not normally take 

 place. The following is one of the most striking observations 

 made on this type of reaction : 



On June 10, 1920, a fragment was cut from a D. spiralis (ani- 

 mal A). This animal was then moved from the field, and a D. 

 vulgaris (animal B) was brought into contact with the fragment. 

 This contact remained for three minutes, after which animal B 

 left the fragment and moved from it to a distance of 200 micra ; 

 but within two minutes it had turned around, retraced its course, 

 and made contact with the fragment again. This time such close 

 contact was made that it appeared as though fusion had resulted. 

 Such intimate relations continued for five minutes, then another 

 separation, animal B leaving the fragment for the second time. 

 After it had traveled about 300 micra it again turned and came 

 back to the fragment of foreign ectoplasm, making a third contact 

 in about three minutes. This time the two objects did not adhere 

 so closely as on previous occasions. Three minutes later animal B 

 moved away from the fragment again, this time remaining away 

 four minutes before returning to make the fourth contact. On 

 this occasion the animal made only slight contact with the frag- 

 ment, moving off again after a few seconds. When animal B had 

 traveled approximately 100 micra, it reversed its course and seemed 

 about to approach the fragment another time. However, before 

 reaching it the animal reversed its course and did not return any 

 more. During the whole procedure (an interval of twenty-six 

 minutes) there was no positive reaction on the part of the frag- 

 ment of D. spiralis toward the D. vulgaris. 



While it is possible that by using different media different re- 

 actions may be obtained, it seems that under conditions comparable 

 to their normal habitat one species of Difflugia will not assimilate 

 protoplasm belonging to another species. 



VII. Will Individuals Fuse with Protoplasm from Other 

 Individuals of the Same Species? 

 Being unable to get cross-fusions between different species, we 



