16 MALL. [Vou XIX. 
are all due to a diseased chorion, which in turn is dependent 
upon endometritis, then we should find embryos tending to- 
wards club-foot, anencephaly, iniencephaly, spina bifida and 
cyclopia, which in fact proves to be the case. However, a 
large group of new monsters, known only to embryologists, 
make their appearance and from the very nature of the abnor- 
mality found but few of them could develop beyond the first 
months of pregnancy. In their study comparisons have been 
constantly made with normal embryos of the same size, and 
in this way, to a certain degree, it is possible to picture the 
order of events. It is found that in these specimens some 
tissues are more susceptible than others, and when the nutri- 
tion of the ovum is impaired it is these that are affected first. 
In very early stages the amnion and embryo are equally 
susceptible and the umbilical vesicle and chorion are the 
most resistant. Later it is the embryo alone, and still later 
the head, central nervous system and extremities. It fol- 
lows then that the parts most susceptible are those most 
frequently found changed, or wanting, in merosomatous non- 
germinal monsters. In general the varieties found in my col- 
lection of young embryos correspond with those obtained 
experimentally by others in birds and appear much like the 
most common human monsters. 
The Saint-Hilaires, who contributed so very much to our 
knowledge of teratology, were the first to study the subject 
experimentally. By a variety of experiments made upon the 
shell of the egg (e. g., pricking and varnishing) the older 
Saint-Hilaire produced a large number of anomalies in which 
there were defective heads and spina bifida. Huis experiments 
were made upon eggs after development was well under way, 
and his results were pronounced enough to allow of com- 
parison with human monsters. The younger Saint-Hilaire 
extended the experiments to include the earliest days of 
incubation, and found that the embryos which developed were 
dwarfed or were wanting altogether. In no instance were 
polysomatous monsters produced. At any rate, the experi- 
ments of the Saint-Hilaires show that a change in the external 
