ON THE POETAL MEMBRANES OP GHELONIA. 1«^ 



reineinb(>r this fact in order t<i understand the relations of some 

 parts in later stages. 



In a slightly older embryo, the sero-amniotic connection has 

 increased more in its vertical extension. Figs. 48 and 48a (PI. VI.) 

 are from the tail region, Figs. 49 and 49^/ (PI. VT.) from the middle 

 of the body. Tn the latter, the sero-amniotic connection is of a con- 

 siderable length, becoming quite definite. 



As to the fate of the posterior amniotic tube. At the stage 

 (Fig. 7, PI. I.) when it is in its highest development, the axis of the 

 tube is the same as that of the embryo, i.e., the embryo and the tube 

 are in the same straight line. Beyond this stage, the tube begins to 

 become curved, at first slightly, then more and more. In Fig. ISa 

 (PI. IT.) the curvature is very slight ; in Figs. 13/> and 8 (PI. II.) it 

 has increased greatly ; in Fig. 9 the distal portion of the tube is bent 

 at a right angle to the proximal basal part ; in Figs. 10 and 15 (PI. 

 [[.), the tube has become very irregidarly curved. It will be seen 

 that the tail end of the embryo which is at first far in front of the 

 horse-shoe shaped distal end of the posterior amniotic tube (Fig. 7) 

 gradually approaches the level of the latter (Fig. 9) until in Figs. 10 

 and 15 it has pushed itself far behind. It is now the distal end of the 

 tube that is in front. This change of the relative positions is no 

 doubt due to the flict that the embryo and the amniotic sac proper 

 grows more rapidly than the posterior amniotic tid)e which they push 

 aside, so to speak, in oi'der to gi-ow beyond it. As the eurvature be- 

 comes greater, ])arts of the tube become fainter and fainter in 

 appearance. For instance, in Fig. 10, a large |)art of the tube 

 excepting the dist;d horse-shaped end and the proximal basal jmrt, 

 was very difficult to recognize (being represented too distinctly in 

 the Figure). In Fig. 15 I could detect only faint traces of the tube, 

 hei-e and there excepting the proximal l)a,sal part which is always 



