46 MALL. [Vor. XIX. 
Ten years ago Born,! in making numerous experiments 
upon frogs’ eggs, occasionally produced cyclopia by splitting 
the head through its sagittal plane after the medullary plate 
is formed and then readjusting the halves. They united at 
once, but in a few instances a double eye was formed. Later 
Spemann? made similar experiments, and he also produced 
cyclops embryos. In some of Spemann’s experiments Triton 
eggs were ligated in the sagittal plane during segmentation, 
and frequently embryos resulted with double heads, one or 
both being cyclops. He believed that this experiment proved 
that the anlage for the cyclops eye was defective from the 
beginning and is not produced by concrescence of two anlages. 
Levy? also produced cyclops embryos by cutting off the front 
of the head of Triton larve. In the course of two weeks 
the two eyes approached each other and formed a double eye, 
but they were not fused; the pigment layer became destroyed, 
or at least was absent at these points. The two optic cups 
touched each other. 
A year ago Harrison produced a new variety of cyclopia 
by removing the entire brain from frogs’ embryos. The eyes 
moved to the back of the head in these specimens and appeared 
to unite into a single vesicle in the region usually occupied 
by the pineal eye. By pricking the extreme anterior end of 
the embryonic shield in Fundulus eggs Lewis found, in 1905, 
that many of the eggs developed into cyclops embryos. All 
stages of eyes were formed, from a double eye, and hour-glass 
eyes with two lenses, to oblong eyes with either two lenses 
or a single lens. The optic cups blended absolutely, thus 
proving the mode of development in these eyes. Lewis 
also found that in many of the embryos the brain had not 
been injured at all, but the prick had destroyed the nose only. 
This experiment shows conclusively that it is the absence of 
tissues between the eye anlages that allows them to come 
*Born, Roux’s Archiv, IV, 1897. 
*Speman, Roux’s Archiv, XV, 1903, and Zool. Jahrbiicher, VII, 
Supplement, 1904. 
"Levy, Roux’s Archiv, XX, 1906. 
