20 MALL. [VoL. XIX. 
account for the separation of the primary cells, thus laying 
the foundation for two embryos instead of one. 
Spemann'® has also produced polysomatous monsters from 
the frog’s egg by tying a ligature loosely around it in the two- 
cell stage between the two blastomeres. Specimens in which 
the ligature struck the median plane of the embryo produced 
two-headed monsters of all grades, their development de- 
pending somewhat upon the degree of the mechanical con- 
striction. He performed similar experiments upon Triton 
eggs, and in some instances found cyclopia in one or both of 
the heads. By broadening the anlage of the tail through 
splitting, a double tail may be formed, or in case limb-buds 
are divided one or more times two or even a cluster of limbs 
may be produced where but one develops normally.“ 
The experiments enumerated above, although not quite to 
the point in the present study, are reviewed because they show 
that teratogenetic problems are solved by experimental em- 
bryology and because they are very striking. If it is clear 
that polysomatous monsters are produced experimentally 
with such precision, the great variety of merosomatous terata 
of the experimenter must be admitted worthy of careful study. 
It is necessary to state this because only a small per cent of 
them live for some length of time, but they show a great sim- 
ilarity with early stages of human terata with which we are 
familiar. A glance at the great works of Dareste and Panum 
makes it clear that the deformed embryos they obtained are not 
easily interpreted and they could easily be pushed aside as not 
bearing upon the subject in question. The same criticism may 
be made against early pathological human embryos. That it is 
difficult to see any marked relation between them and monsters 
at the end of pregnancy caused me much confusion for a 
long time, but after studying a large number of deformed 
embryos I am finally convinced that the pathological embryos 
are nothing but young monsters. This conclusion is sup- 
*Spemann, Stizungsber. d. phys.-med. Gesellsch., Wurzburg, 1900; 
Zool. Jahrbuch, VII Supplementband, 1904. 
“Tornier, Roux’s Archiv, XX, 1905. 
