No. 2.]| DEVELOPMENT OF THE HUMAN COELOM. 407 
of the somatopleure and splanchnopleure are still united, and 
mark the place of the formation of the rudimentary allantois. 
Having carried the development of the human ovum to this 
stage by means of hypothetical stages, based upon the develop- 
ment of Pteropus, I can now continue the description of the 
development based upon observation. 
Abnormal Ova. — Teratologists are accustomed to view a 
group of abnormal states as arrested development, and in 
recent years a number of abnormal human ova have been 
studied by His,1 by Giacomini,? and others. Frequently in the 
ee 

Fie. 5. Fic. 6. 
Fics. 4-6. — Hypothetical Stages of the Early Development of the Human Ovum. A&, Rauber’s 
layer ; ec, ectoderm ; ex, entoderm ; »zes, mesoderm; # v, umbilical vesicle; coe, coelom; 
all, position of allantois. 
development of an ovum the embryo is destroyed completely, 
or, according to Giacomini, may wander out of the ovum. 
In these cases the ova are aborted. Frequently, however, a 
portion of the embryo is not developed, or it dies and the 
remaining portion develops for a time, and then the ovum is 
aborted. I have now in my collection a beautiful example of 
an ovum of apparently normal structure, the interior of which 
is lined completely with an amnion, and in place of an embryo 
1 His: Anatomie mensch. Embryonen, Heft 2, 1882, and Internationale Beitrige 
zur wissenschaftlichen Medecin, Bd. 1, 1891. 
2 Giacomini: Ergebnisse der Anatomie und Entwicklungsgeschichte, Bd. 4, 
1895. The original papers of Giacomini are in the Archives Italiennes de Biologie, 
vols. X VITI-XXII. 
