DICHOTOMY. 115 
monsters, and endeavour to show that they arise from 
dichotomy, partial or complete, of the trunk-axis of the 
embryo. Before describing actual specimens it will be 
well to adduce facts in support of the view that double 
embryos may arise from a single ovum. ‘ae 
In 1869 Haeckel?! showed that it was possible, bys em 
ews 
/ 
Fic. 63.—A Sheep with supernumerary fore-leg. 
dividing artificially the eggs of Crystallodes rigidum to 
multiply the number of embryos. The experiments | 
were very simple, and consisted in taking a Crystal- | 
lodes larva on the second day, in which the amceboid | 
movements were very lively, placing them in a watch- 
glass with sea-water, and with the aid of a simple micro- 
* “ Zur Entwicklungsgeschichte des Siphonophoren.”’ Utrecht, | 
1869. 
