132 J. A. DAWSON 



3. THE OCCURRENCE AND BEHAVIOR OF DOUBLE ANIMALS 



During the progress of the previous work (part I), while 

 studying a six-day-old mass culture made on July 20, 1917, from 

 a stock slide of culture A, numerous pairs were observed, while 

 many individuals were still dividing by fission. In addition to 

 the paired animals which were apparently attempting to conju- 

 gate (pp. 482, 483. part I), three pairs of animals were found 



Fig. 1 Normal twin drawn from life, magnified about 700 diameters, showing 

 ventral surface of one animal and a portion of dorsal (aboral) surface of the other. 



evidently fused in what appeared to be a very unusual manner. 

 These were isolated and the next morning were found to have 

 divided twice, giving in one case four double animals exactl}^ 

 similar to the parent double animal. These animals thus iso- 

 lated formed the ancestors of the four lines of a culture (AT) which 

 was carried with the object of studying later developments in 

 the life-history of these 'abnormal' forms and for the purpose 

 of comparing their rejiroduction with that of the animals in cul- 



