AND THE FOETAL MEMBRANES, IN THE CHICK. 349 



iiect tlie two cîivitiey, mid appears «ieve-like. Figs. 85-87 are from a 

 series of sections throiio-h a perforated sero-amniotic connection of the 

 twelfth day. In Fiir. 85, which is the most anterior represented, the 

 connection is entire and intact. In Fig. 86 it is very thin. In Fig. 

 87, there is a perforation. 



These pores in the plate-hke connection grow larger in size in 

 later days, while the niunl^er becomes less by the running together of 

 some adjacent ones. At length, after the sixteenth or seventeenth 

 day the two sides oi' the plate are connected only by a few sti-ands 

 which remind us of the cliordae tendineae of a mammalian heart 

 (Figs. 54-56). 



Thus the epiblast of the annii(jn and that of the serous envelope 

 again become continuous ; the exti-a-embryonic coelomic cavities of 

 the two sides are as completely separated from each other throughout 

 the entire extent of this sero-amniotic connection as in any previous 

 stage. 



6'. SuppU'iiieni to tlic I'recediiKj Sections. 



1 will now make some necessary remarks on other points Avhicli 

 it was convenient to witlihold until I had traced, in the preceding 

 sections, the main course of the changes in the connection itself. 



In the extra -embryonic part, near the sero-amniotic connection at 

 least, the epil)lastic cells can usually be distinguished from the meso- 

 blastic cells by the following points. In form, the mesoblastic cells 

 are flattened in the plane of the layers themselves, wherever the 

 cells are densely disposed, and are stellate, wherever the number of 

 cells is very small, wliile the ejnblastic cells are mostly ])erpendiculai- 

 t<j the phine of the layei's (Figs. 75, 80, 85, and DO). Conse- 

 (piently the mesoblastic tissue is schistose or reticulated, while the 

 epiblastic layei's are in more or less regular strata and compact. 



