394 General Notes. [April, 
been described by Hoffmann! in Axas boschus, in which the can- 
alis neurentericus is shown (pl. 111, fig. 5) to open into the intes- 
tine while a canal also extends from it anteriorly into the chorda 
itself. Such is essentially the arrangement in the specimen here 
described, except that the chorda has been differentiated along 
the entire extent of the neurenteric canal. 
latter joins the primitive streak. A narrow diverticulum from 
this passage is continued forwards for a short distance along the 
axis of the notochord. After traversing the notochord, the pass- 
age is continued into a hypoblastic diverticulum, which opens 
ventrally into the future lumen of the alimentary tract.” It is 
clear from the figure that this must have been the case in the 
specimen here under consideration; that is, the neurenteric pass- 
age about which notochordal tissue was differentiated was con- 
tinued forward into the chorda, as the latter was folded off from 
the hypoblast, and that from this passage in the chorda one pass- 
ing downward to the intestine was given off about which noto- 
chordal tissue was also differentiated. 
. While it is highly probable that this embryo chick displays 
an archaic development of the chorda, yet the facts are significant, 
especially when viewed in the light of the interpretations of 
- Ehlers as to the significance of the “ Vebendarm” in the inverte- 
brates. This specimen shows that what must have been a part 0 
P, the neurenteric canal during an earlier stage, 7. e., Ch’, has been 
æ actually differentiated into a structure histologically identical with 
- the true axial notochord Ch. 
This specimen is therefore of great interest, since it demon- 
trates, if we may regard it as representing a palingenetic condition 
of development, that the chorda dorsalis was primitively in abso- 
lute continuity with the intestine (mesenteron) posteriorly, and 
that there may therefore have been primitive Chordata in which 
chorda was usually developed as such, in almost absolute 
continuity with the alimentary tract—/ohu A. Ryder. 
PROFESSOR SELENKA ON THE DEVELOPMENT OF THE OPossUM 
- (DIDELPHYS VIRGINIANA). — The following short notice of the 
recent investigations of Professor Emil Selenka, of Erlangen, on 
` the development of the common opossum, although it has ap- 
_ 1 Die Bildung des Mesoderms, die Anlage der Chorda dorsalis und die Entwicke- 
jung ¢ Canalis neurentericus bei Vogelembryonen. aturk, Verh. der Ko 
Akad. Wetensch. XXII, Amsterdam, 1833. + 
