SOME PHASES OF THE GASTRULATION OF THE HORNED 
TOAD, PHRYNOSOMA CORNUTUM HARLAN. 
BY 
CHARLES L. EDWARDS AND CLARENCE W. HAHN. 
From the Biological Laboratory, Trinity College, Hartford, Connecticut. 
WitH 15 Trext FIGURES. 
The following account of the gastrulation of this very interesting 
iguanid is the outcome of investigations carried on at the University of 
Cincinnati in 1899 and 1900 and at Trinity College in 1900 and 1901. 
The embryos were collected at Austin, Texas, in 1892-1894. Except for 
the cleavage and the beginning of gastrulation the collection embraces 
the complete embryology of Phrynosoma conutum, but in this paper we 
present only the general phenomena of the gastrulation as interpreted 
from the stages in our possession. The breeding and nest building habits 
of the horned toad have been described by Edwards, 96. Breeding takes 
place in the months of June, July and August. Contrary to all pre- 
vious accounts in which species of the genus Phrynosoma are given as 
Viviparous* it was observed that at least in the case of P. cornutum at 
Austin, Texas, the eggs, numbering in some instances as many as twenty- 
five, are deposited in nests formed in a chamber at the end of a tunnel 
in the ground which the female burrows, and then, after laying the eggs, 
carefully refills with the loose pellets of earth. At the time the eggs are 
laid the embryo has attained the stage in ontogeny equivalent to that 
represented by Peter, 04, Taf. II, Fig. 17, as N. T. Nr. 68 for Lacerta 
agilis. The Phrynosoma embryo when it leaves the oviduct is 2 mm. in 
its greatest length. The head bend forms a wide acute angle at the pro- 
jecting mid-brain, while the neck bend forms an obtuse angle. The body 
is slightly curved, the caudal end being twisted around to the right. In 
the open space of half the length of the body between the tip of the fore- 
brain and the tail lie the well marked, distended allantois and the 
strongly curved, prominent heart. 
In order to obtain the earlier stages, it is necessary to take the eggs 
1This error, repeated by Gadow, o1, Dp. 533, was corrected by Edwards, 03, 
p. 826. 
AMERICAN JOURNAL OF ANATOMY.—VOL. V. 
