ON THE FOETAL MEMBRANES OF CHELONIA. 35 



is not to be olearly distino-ui.slied. The ])]ace where it should be 

 present is drnwn ont to ;t point (Fio-. 26, PI. IV.): thnt seems to be 

 all the indication I'emninino- in later stao-es of rhe posterior rube (tf 

 the amnion. 



The white remains to the last in Tricmvx ns in (MeniTnys. 

 !ind is found opposite the triana'idar area of the \entr;d |iole left un- 

 covered by the allnntois. This |)nrt is o'enerally more or less 

 depressed to receive the nr^iss which is sticky niid yellowish. The 

 outermost cells of the serons enxelope in this area imdero'o modificn- 

 tions similnr to those of the corresponding' spot in Clemmy s . Tlie\' 

 become taller and lar^'er and contain large vacuoles, their nuclei become 

 larger and irreo-nlar in shape and stained deeper (Fig. S4(f., Comp. Fig. 

 29, PI. ÎA'.). In Tri onyx howe\ er. there appears to be no process 

 that penetrates into the white as in Clem my s . 



The yolk passes inside the embryo in hatching. 



Of the completed fœtal membranes of Clemmy s and Tri onyx 

 above described, there can be no doubt that Clemmy s has retained 

 more primitive relations. The main ground for this (Conclusion is that, 

 starting from the same ipoint, (bfferent structures (above all, the sero- 

 amniotic connection) retain in Clemmy s tlieir original positicni and 

 arrangement, while in Tri onyx various structures are disturbed 

 from their first arrangement, the sero-amniotic connecticm being pushed 

 forward, l)ent and C(^m])ressed into a secondary shape. If the process 

 begun in Tri onyx were to go one step further, no spot would be 

 left uncovered by the alia uteris, the sero-amniotic coiniection might be 

 pressed out of existence, the two allantoic lohes might come in (^ontact 

 with each other, and then the condition liitherto accepted as occurring 

 in Birds would be the result. 



