PRODUCTION OF TWINS AND DOUBLE-MONSTERS 349 



but that the developmental momentum was so seriously slowed 

 down that dedifferentiation of the original symmetry relations 

 occurred, and, when recovery came, the unity of the organi- 

 zation had been lost, giving an opportunity for the redifferen- 

 tiation of two independent apical points and the consequent 

 twin development. 



Wilson ('11), in his classic book on the cell, describes and 

 figures various phases of twinning in Amphioxus, which remind 

 one strongly of the conditions described for Patiria. Not only 

 were dwarf larvae produced, but gastrulae with paired arch- 

 entera occurred not infrequently. Some of the earlier stages of 

 twinning are seen in which it is obvious that, as in Patiria, the 

 blastomeres of the two-cell stage had become physiologically 

 isolated, each following its own cleavage plan, and destined to 

 form double blastulae or gastrulae, either isolated or conjoined. 

 The experimental procedure was the familiar one of shaking the 

 eggs when in the two-cell or the four-cell stages. When the 

 shaking was sufficiently violent blastomeres were physically 

 isolated and produced separate dwarf larvae; but if the shaking 

 was less severe the blastomeres were only physiologically iso- 

 lated to varying degrees and various types of double monsters 

 resulted. Wilson does not say definitely that the shaking was 

 followed by retardation, but the inference is that the shaking 

 caused a disorganization of the bilateral symmetry relations 

 existing between the blastomeres of the two-cell stage, and the 

 consequent redifferentiation of two apical point and two separate 

 axes. 



An interesting case of twinning in plants was brought to the 

 writer's attention last June. In the Santa Clara Valley of 

 California many peach trees bore considerable percentages of 

 twin peaches. These consisted of various stages of double 

 fruits, some almost entirely separate, others merely constricted 

 as to the fleshy parts. On inquiry, it was learned that at the 

 flowering season a severe cold spell had occurred in this region, 

 and this was held to be responsible for the twinning in the fruits. 

 How could this be explained? A theory might at least be 

 postulated to clarify the situation. The unusual cold probably 



