
838 The American Naturaist. [September, 
EMBRYOLOGY. $ 
Notes on the Development of Engystoma.—This interesting 
Batrachian occurs in the Piedmont section of North Carolina, near 
Littleton, and within twelve miles of the southern boundary of 
Virginia. Its presence after a rain may be discovered:by its peculiarly 
plaintive note. Oviposition seems to occur in the evening and during 
cloudy afternoons. It is now late in July, yet two lots of ova have 
been found by me which had been very recently deposited by the 
parent female ‘‘ frog-toad,’’ as it is known here amongst the natives. 
The eggs are heavily pigmented at the upper or animal pole, being 
darker than the eggs of Rana, and also considerably smaller. They 
are laid in strings, but so coiled as to form a nearly complete single 
layer over aconsiderable surface of water. The gelatinous coating, as 
in Rana, spreads out under the surface of the water, where by its 
adhesion to the layer of molecules at the surface a certain amount of 
support is thus gained for the eggs. It is therefore evident that surface 
tension is an important agent in keeping the eggs of this genus, and 
those of Rana, at the surface of the water. Other genera, such as 
Bufo, do not have the eggs supported on the surface, but are laid in 
strings formed of one row of eggs, wrapped in a gelatinous cord which 
lies on the bottom of the pond in which oviposition occurs. Still 
other forms have the eggs glued together in large masses and supported 
upon water weeds; this is notably the case with some Urodeles, 
such as Amblystoma. : 
The development of the eggs of Engystoma is rapid; three days 
after deposit the larvee escape from the egg-envelopes. Throughout 
the course of development there is well-marked evidence of geotrop- 
ism, or of the action of gravity in maintaining the equilibrium of the 
egg. The animal or black polé remains uppermost, the heavier or 
light-colored vegetative pole remains lowermost ; the whole egg is thus 
maintained in a position of static equilibrium with the earth’s center. 
There seems to be no tendency to rotate the egg through ciliary action, 
previous to the closure of the medullary folds. That cilia are entirely 
absent on the eggs of Engystoma is proved by the fact that at the 
-time the medullary groove is still open every egg of the same age is 
in exactly the same position in respect to the center of the earth, and 
remains so for a long time, or until the tail fold is well developed and 
the medullary groove has been closed. Before the closure of the 

