ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
66 ; 
the eighth thoracic segment caudal wards the V. azygos is a secondary 
formation. The caudal portion of the right cardinal, after it has altered 
its relation to the ureter, remains as the cardinal portion of the postcaval 
from the entrance of the renal veins caudalwards. The proximal portion 
of the postcaval is formed from two distinct parts, a proximal part 
arising from the union of the Y. omphalo-mesenterica and the Y. umbili- 
calis dextra and a caudal part which represents an anastomosis between 
the cardinal veins and the proximal part of the postcaval. Of the left 
posterior cardinal there is usually no trace left in the thoracic region ; 
in the abdominal region it persists either between the V. lumbalis trans- 
versa posterior and the Y. renalis sinistra, or as a continuation of the 
left spermatic. The pelvic portion, of the cardinals is modified by fusion 
in the common internal iliac. The caudal portion persists on one side 
or on both sides as the caudal vein (sacralis media). 
Sero-Amniotic Connection and Foetal Membranes of Chick.* — 
Mr. S. Hirota describes these structures in the Chick, and compares 
them with the same parts in the Chelonia. The essential points in 
which they agree may be summarized thus : — 
(1) The 'chick has, at the posterior edge of the amniotic fold, a 
constant deltoid area free from the mesoblast ; this is observed in com- 
paratively later stages in Chelonia. 
(2) As long as the amniotic fold grows posteriorly, the sero- 
amniotic connection and the remnant of the epiblastic deltoid area is 
equally prolonged posteriorly until it becomes a long string. 
(3) This connection is more or less widened on both sides of the 
epiblastic bridge by the entrance of the mesoblastic tissue. 
(4) The epiblastic layers of the extra-embryonic parts are stratified, 
at least near the connection. 
(5) The connection between the serous envelope and the amnion 
persists during egg-life, and there is no direct continuity between the 
extra-embryonic coelomic cavities of the two sides along the length of 
the connection. 
(6) The growth of the allantois is greatly influenced in later stages 
by the sero-amniotic connection. 
The essential points of difference are — 
(1) In the Chick the amniotic fold arises at a comparatively later 
stage than in the Chelonia, and has no conspicuous area free from 
mesoblast. 
(2) In Chelonia the epiblastic delta of the amniotic fold is always 
larger than that of the Chick, but in the latter it is enormously thickened 
dorso-ventrally. 
(3) In Chelonia there is no proper tail-fold, while the Chick has no 
trace of the posterior tube which forms so conspicuous a feature of the 
Chelonian amnion. 
(4) The epiblast bridge of the connection seems to be persistent in 
Chelonia, while in the Chick it is replaced by mesoblast. 
(5) The sero-amniotic connection is not perforated in Chelonia, and 
it is not enclosed within the foetal membranes, as these Eeptiles have no 
albumen-sac. 
* Journ. Ooll. Sci. Imp. Univ. Japan, vi. (1894) pp. 337-70 (3 pis., 16 figs.). 
2 z 2° 
