285 
doubtful tone adopted in mentioning the point in the latest text-book 
on te subject, (Quarn’s Anatomy, 10 th. Ed.) it seems that further 
observations carried on another class of the Amniota are far from 
unnecessary. 
From the study of seven chicks in serial sections three points 
are demonstrated : 
1* The continuous cavity of somite and coelome certainly does 
exist for a short time. 
2% It is confined to the three (possibly four) anterior segments 
in chicks, with from 12 to 20 somites. 
3% The course of the cardinal veins has something to do with 
the obliteration of the connection between the two extremities 
of the originally continuous cavity. 
1* Figure 1 illustrates the first point and needs but little de- 
scription. It is taken through the third somite of a chick with 12 
protovertebrae, and, as the plane of the section is not exactly trans- 
verse, and yet appears to lie very nearly in the plane of the commu- 
nication of the two cavities, it shows that this connecting cavity does 
not lie exactly at right angles to the median line of the chick. Sec- 
tions from other chicks in the same stage show a similar condition, 
but in the specimen figured the point is seen more clearly than usual. 
From the fact that the communication is confined to only three or 
four consecutive sections, we see that the communication is not a cleft 
extending the whole antero-posterior length of the somite, but is 
rather a hole situated slightly in the posterior half. It is to be noti- 
ced that the cavity is perfectly clear and open throughout its whole 
length: in a similar section figured in Quain’s Anatomy, tenth edition 
Fig. 139, it is seen to be filled with something, just what is hard to 
say as the drawing is very indefinite. 
In slightly older stages (about 20 somites) the connection is still 
evident although the actual cavity no longer exists. The edges of 
the somite have been brought together, but that the cavity between 
them was a portion of the coelome is clearly shown by the fact that 
the tissue of the protovertebra is perfectly continuous with the meso- 
thelium lining the body cavity (Fig. 2). In chicks with less than 
about 12 somites or more than about 20, I have not found above 
described conditions. 
2° That this connection is confined to the first three (in one case 
four) segments is shown by very little observation. Fig. 4 (taken 
from the fourth segment of a chick with twenty somites), shows that 
neither the actual communication nor the mesothelial connection exists 
