PRODUCTION OF TWINS AND DOUBLE-MONSTERS 



333 



near the basal end, and of equivalent size. Such larvae as this 

 live for days unchanged. Figures 26, 27, and 28 show three 

 conjoined twin larvae in which the paired archentera are formed 

 nearly at right angles to the original primary axis. In the larva 

 shown in figure 28 both archentera have taken the initial steps 

 in the development of the hydro-enterocoel vesicles, but the 

 process was never actually accomplished. 



25 



26 



27 



28 



29 



JO 



3r 



Fig. 25 A symmetrical twin larva with both archentera growing in near the 

 original basal end. 



Figs. 26, 27, and 28 Types of symmetrical twin larvae with archentera grow- 

 ing in from opposite sides of the larva. These are all mirror-image duplicates. 

 (Figs. 29 to 37 are from hybrid cultures) 



Figs. 29, 30, and 31 Relatively large active larvae with well-differentiated 

 primary archenteron, but comparatively poorly developed secondary archentera. 



