ox THE FOETAL MEMBliAXES OF CHELOXIA. 



25 



I'uiljryo. The aljunluis hus spread over the larger part of the yolk 

 ï>u that, ill the tigure, the latter show.s bare only at the posterior part 

 of the ventral .--ide. The figure shows the left lobe of the allantois, 

 the sero-ainiiiotic (-«Mjiiection with peculiar structures at its posterior 

 cud. and the left set of allantoic Aessels with the corresponding incision 

 in the margin of the alhnitoic vesicle. 



ViiS. 7(1 gives a, \ entrai \iew of an cjj;^^' of aliout the same stage. 

 Tlie rlifee lo1)es of the allantois have n<.)W spread themselves over a 

 jiart of the lower half and are here \ ery conspicuous. The lol)e that 

 a])prar> to ilie ol)server's right is tlie left allantoic lol)e. Xext to it 

 is the middle lobe and finally at the o]>server's left is the i-ight 

 allantoif lobe. The incision between tlu' middle and the right lobes 

 is the anlei'ioi- constriction of Figs. ()7 and 68, and at its dorsal end 

 is found the I'iuiit set of* alhnitoic vessels. The incision between the 

 middle and the Icfi lohes passing o\er the head of the embryo 

 correspontls to ihc postcrioi- constricrion of the; earlier stages, and 

 has the scro-anmiotic connection placed in it. While in Figs. 67 

 and C)S the cnd)rvo is coiihned to the space l)elow the middle loljc, 

 in this hgiirc ihc head <d' the end;ryo appears below the left lobe 

 lo the left of the sero-amniotic connection. This is brought about 

 by the following circiuustances. In Fig. 67, the embryo lies on its 

 left side and, the sero-amnioti(.- connection l)eing a[)proximately over 

 its dorsal median line, we are viewing it. so to s[)eak, from the side. 

 As the embryo and with it the amnion gi'ow, the embryo comes 

 again to lie on its ventral surface, a> in the earliest stages, and the 

 seroamniotic connection ag;iin accomipanying the dorsal surface <^f the 

 eml)ryo is tiu'ned toward the obser\'er. 'Idle amnion is thus free to 

 grow to the left of it, under the left allantoic lobe. The amnion 

 being spacious, the eml)ryo is aT)le to mo\e within it, and the head 

 may now be seen to the left, or to tlie right, or directly under, the 



