ON THE FOETAL MEMBRANES OF CHELONIA. 



i>7 



shallow notch prorluced by the posterior (the leff) set of blood-vessels 

 in Fig. 67, or to the inrision in Fig. 60. Hence, at its distnl end the 

 posterior or left set of allantoic vessels is found. The seam that 

 separates the middle fi'om the left allantoic lobe is difterent from the 

 other two, for here the two lobes of the allantois cannot come into 

 contact, being separated bv the sero-amniotic connection. Ft passes 

 over to the dorsal side of the embrvo (Fig. 71), and its dorsal end 

 has the triangidar i-emnant of the postei'ior tube of the amnion, 

 and the peculiar conical white streak caused by the simple incision 

 of the allantois. (Compare Figs. 68. PI. V[TT., and 12, PI. 11.). 



There is one featnre in an e^»; tliiis advanced which deserves 

 special notice. The white of the egg which disa])peared vei-y early iVom 

 over the embryo continues to grow smaller and smaller in rpiantity. 

 But it persists up to a very late date, if it ever disappears entirely. 

 There is alwavs, even in very much advanced eggs, a 

 small mass of the white just at the point where the 

 three lobes of the allantois meet at the lower pole. This 

 mass seems t(^ have undergone some change in its chemical composition 

 for it is now much denser, slightly yellowish in color and sticky. 

 To receive this mass the mend^ranes are often shallowly depressed. 

 Into the center of this mass of the white a thick low ])rocess of the 

 membranes penetrates (shown in Fig. 71« on the left allantoic hdie, 

 just to the right of the sero-amniotic seam), so that when the 

 membranes are removed, the mass of the white with the central part 

 hollowed out appe;u-s like a bowl. The cells of the serous envelope 

 on the surface of this process are peculiarly modihed. They are more 

 columnar than in other parts (Fig. 21», PI. IV.). Their nuclei are 

 larger, irregular in shape, and stained deeper. In these cells are found 

 many large vacuoles which remain unstained. There can l»e n<^ 

 doubt that these cells are absorbing albuminous particles from the 



