44 MALL. [VoL. XIX. 
them up to the total estimated number of pathological ova 
per 100,000 pregnancies. “Deformed heads” I have paralleled 
with “hydrocephalus,” but I do not mean to infer that one is 
directly related to the other. Otherwise the subdivisions 
coincide. It is remarkable that in each instance there are 
about six of a given variety of embryonic monsters for each 
at full term. At any rate, the constancy of the ratios speaks 
volumes in favor of the genetic relation of monsters to path- 
ological embryos. 
In my collection there are five specimens of exomphalos 
(Nos. 115, 162, 166, 244 and 364), mostly in very young 
stages, in which there is an extreme degree of atrophy ot 
the embryo. It is a question whether any of these embryos in 
which the atrophy is so extreme could possibly have lived much 
longer, for in them the body of the embryo is nearly de- 
stroyed. 
In many of the specimens there is a marked distention of 
the central nervous system, and it would probably be more 
to the point if they had been classed with hydrocephalic 
monsters. The frequency with which hydrocephalus and 
dilatation of the embryonic nervous system are encountered 
makes it questionable whether anything is to be gained by 
the comparison. 
As Giacomini has pointed out, the amnion is sometimes 
partly destroyed or is wanting entirely. More often, how- 
ever, there is hydramnios, as is also the case with monsters. 
The excessive secretion of fluids into the cavities of the body 
and into the amnion is often accounted for by a supposed 
interference with the circulation, and this theory is supported 
by removing the heart in young tadpoles (Knower’s experi- 
ment), which is always followed by general dropsy. 
To come back to the deformed heads, in which there is not 
only an arrest of development, but also an actual destruction 
of many of the tissues, the head is more or less necrotic or 
stubby, often the brain is exposed, either in front or over the 
mid-brain, or the whole brain may be wanting. In some 
cases the lumen of the brain communicates directly with the 
