No. 1.] ORIGIN OF HUMAN MONSTERS. 41 
cartilage of the cord is of quite common occurrence among 
the normal embryos of my collection. I have looked through 
the normal embryos of about the same stage as No. 6, and in 
no instance have I found one with a vesicle like it attached. 
Among the specimens two occur with very small vesicles at 
the extreme tip of the cord, this being best marked in No. 22, 
an embryo 20 mm. long. Another embryo, 19 mm. long, 
No. 220, also shows this dilatation. It seems to me that in 
these cases there is only a slight exaggeration of the normal, 
while in No. 6 the vesicle is newly formed. 
While the per cent of cases of spina bifida among patholog- 
ical embryos and fcetal monsters is about 7 per cent of the 
total number of monsters in each case, it rises in anencephaly 
to about 20 per cent, that is, in 1,000 pregnancies there are 15 
cases of anencephaly aborted very early and one case goes on 
to full term. 
Among the embryos with changes in the brain that indicate 
the beginning of anencephaly there are many varieties of 
deformed brains that are exposed more or less. The brain 
may be escaping from the front of the head, the mid-brain 
may be exposed, or the medulla is distended and fills the 
whole atrophic head, as the various figures show. In most 
of the specimens there is a marked histolysis of the surround- 
ing tissues as well as of those of the brain, with vascular 
metamorphosis of the brain tissue, as is shown in specimens 
like Nos. 364 and 365. In these cases we cannot speak of a 
simple arrest of development only, but also of a destruction of 
tissue, histolysis and necrosis, or parenchymatous inflamma- 
tion, as Panum would call it. These specimens are discussed 
sufficiently under various headings further on, and under the 
descriptions of the embryos in the last portion of this paper. 
It has been shown that typical spina bifida and anencephaly 
can be produced in a number of species of amphibia by Mor- 
gan’s experiment, that is, by cultivating the eggs in dilute 
solutions of NaCl. This causes an arrest of development of 
the embryo, which is decidedly more marked in the central 
nervous system than elsewhere. There is also a more or less 
