782 The American Naturalist. [September, 
EMBRYOLOGY. 
Spina Bifida and the Blastopore.’—Prof. Oscar Hertwig has 
made an important contribution to teratology and attempted the solu- 
tion of some fundamental morphological problems in a paper that is 
disappointing from many points of view, though undoubtedly of con- 
siderable value. 
In order to produce polyspermy in the frog, eggs were kept two to 
four days in a moist chamber before artificial fertilization was 
attempted, or else the female frogs were isolated for four to six weeks. 
In either case very many eggs developed normally, yet it is assumed 
that the hundred monstrous forms picked out were the results of some 
injury made upon the egg by the above treatment and that polyspermy 
took place. 
This latter assumption is in no wise supported by any direct obser- 
vations, but rests merely upon the previous work done by the author 
and others upon other eggs. 
Passing over some interesting cases of irregular and of partial 
cleavage we will briefly describe the three sorts of monstrosities assumed 
to be imperfect conditions of gastrula stages. 
In the first case there is a large yolk plug appearing at the surface 
of the embryo all along the dorsal, median region, so that such a 
monstrous embryo of five to seven days looks as if there were a huge 
blastopore with a medullary fold along each side of it and a plug of 
yolk cells projecting between these folds. At each end of this plug a 
depression leads ventrally, a sort of fore gut and hind gut. At the 
posterior end two elevations represent a sort of double tail. In fact, 
the medullary groove or tube and the notochord are double and pass 
along each side of the yolk plug. ; 
In a second set of abnormalities the embryos have advanced so far 
as to have eyes, external gill slits, a short tail and a heart. The tail 
is bent up at right angles to the trunk and anterior to it is a small 
plug of yolk coming to the surface on the median dorsal line. Inter- 
nally the nerve tube and the notochord are double on each side of the 
yolk plug, or open blastopore, but anterior to that form normal, single 
structures. Posteriorly they run as paired organs into the tail, which 
‘Edited by Dr. E. A. Andrews, 
*Archiv f. mikros. Anat., xxxix, 1892, pp. 353-492, plates 16-20. 
