DEVELOPMENT OF THE CHICK THIRD PERIOD. 331 



The intestine makes several turns outside of the umbilicus, 

 and continues in communication with the vitellary sac by 

 means of the vitellary duct ; upon the inner surface of the 

 vitellary sac, and over the tortuous veins, membranous pro- 

 ductions puckered or wrinkled folds make their appear- 

 ance ; and at the same time similar formations occur upon the 

 mucous membrane of the intestine. The allantois has now 

 grown completely around the embryo, so that the ovum the 

 vitellary sac, the remaining albumen, &c. included is com- 

 pletely enve- 

 loped anew as 

 it were, and will 

 now retain its 

 form even after 

 the shell is re- 

 moved (fig. 3 54, 

 b ; from the 

 Kestril Falco 

 ti mm nc a I us) ; 

 the serous co- 

 vering disap- 

 pears. 



[ 497. In 

 the beginning 

 of the third 

 week, the em- 

 bryo, straitened 

 for room, from 

 the transverse 

 axis of the egg 

 comes more and. 

 more into the 

 long axis, which 

 it finally fills ; 

 the head is 

 turned towards 

 the bn-ast, and 

 mostly lies un- 

 der the right 

 wing ; the al- 

 lantois has inclosed the whole embryo and vitellary sac, and 



Fig. 354. Embryo of the Falco tinnunculus, 

 much farther advanced than that of the fig. 353. It 

 is represented enclosed in its membranes, and of the 

 natural size ; hut heing removed from the shell, its 

 weight has caused it to spread, and to look longer 

 than it is in fact. The embryo of this falcon, by 

 reason of the transparency of the membranes, is pe- 

 culiarly fitted to serve for the demonstration of the 

 relative position of the several parts : a, the embryo 

 shining through the membranes ; /, /, the eyes of 

 great size, seen from above ; b, b, the allantois, has 

 grown completely around the embryo, and so forms 

 a perfect envelope, the chorion, whose principal vas- 

 cular branches are perceived ; c, c, the amnion ; d, d, 

 the yolk-sac ; e, the albumen ; g, the coccyx, with the 

 feathers beginning to sprout. 



