1836. | Embryology. 393 
sections consist of a vertical longitudinal series, which show the 
structural details represented in the accompanying figure, drawn 
with the aid of the camera lucida. 
The most striking feature is the condition of development pre- 
one, CAY., e ventral 
lation to the hindermost 
vou spinalis M ; vesicular cavity just above the 
th ? cord N. ; In fact, int of union between the medulla spinalis and 
ere iS a readily trace- chorda, and representing a dilatation of the neur- 
able bridge of tissue be- enteric canal; Nc’, medullary canal; Z and /, 
tween the end of CRO and posterior part of mesenteron; Zr, proctodzeum. 
: Bi 
the under side of WV, which x 
conclusively demonstrates that these two structures were at an 
earlier stage continuous, Just above this bridge of tissue there 
S a cavity, Ne, which must in all probability be regarded as a | 
sa le at this point. Certain sections of this series, from 
etd different plane, show that the nervous cord N extended a 
somewhat beyond the point where the notochord joined it, 2 
gure, though there are somites developed beyond its termination. 
udging from what has preceded, it is evident that a connection 
wad ‘cen the central neural canal Wc’ and the developing chorda 
ia Serna once existed in this embryo. The central canal Nd 
which ae a traceable to the cavity Vc farther back, just below — 
ian € neural tube is continuous with the chorda. It seems, — 
the ch not improbable that the single point of connection between — 
ieee canal, orda and nervous cord represents the atrophied neurenteric — 
dowi Ta that the portion of it which joined the intestine passed 
ofp ough Ch” and Ch’. Even supposing that the condition 
S Rasy S observed in this particular embryo is not normal, it is 
-type eee that this specimen may represent a palingenetic 
ves OF avian development, comparable with such an one as has 
s 
