1 898 - 99 . J Mr T. H. Bryce on Duplicitas Anterior. 
625 
of the ventral coelom, at a point where that cavity still consists of 
two separate portions as in a normal embryo — in fact, at the point 
where the head fold proper ceases, and where the lateral folds 
begin to unite. From the 94th section to the 121st, the neural 
plate is single, but there are two canals bounded by three folds, a 
mesial and two lateral (fig. 4). The mesial fold consists of two 
parts, which, as the neural plate becomes more and more limited, 
and the neural canals approach one another, come nearer together 
and finally fuse to form a solid septum, which in turn disappears, 
and a single large canal is formed with gaping medullary folds 
(fig. 5). Further back the medullary folds approach more closely 
again, but nowhere unite (fig. 6). Section 263 (fig. 7) shows that 
the floor of the now widely open neural canal is indented by two 
shallow grooves above the two notochords, which are separated by 
a mesial thickening of the common neural plate, and when 
followed backwards are seen to be continued into the two grooves 
described above. 
The Fore-gut consists, at the anterior end, of two entirely separate 
tubes, but, in the 75th section, their mesial walls come in contact, 
and a few sections further back there is only one very broad and 
compressed cavity. The lateral parts of the ventral coelom are 
here very far apart (fig. 2), and in a mass of mesoblastic cells 
between them are seen two spaces which unite in section 96 (fig. 3) 
to form a single cavity, again to separate further back, where the 
splanchnopleuric folds begin to part. In a normal embryo, the 
two anterior cul-de-sacs of the ventral coelom do not unite until a 
later stage opposite, or rather under the heart anlage. The two 
halves of the primitive heart tube are still wide apart (fig. 4), for 
the splanchnopleuric folds have parted in front of the heart anlage. 
It is also to be noted that the primitive heart tubes are abnor- 
mally broad and flattened out. 
In the three cases of double chick embryo belonging to this 
class, cited above, as well as in the monstrous human embryo of 
Laguesse and Bue, there were two notochords, though in Kaestner’s 
embryo they came in contact at their posterior ends. In Kaestner’s 
case and in Hoffman’s, there was only a single neural plate 
throughout, folded in the latter into two canals at the anterior 
end, while in the former the canal was single along its whole 
