IS 



K. .Ml'I'SUKUi;!. 



iKtw jtisl ;il flic cdiic (»1 tlic \as(;iilar area. Tli«' I'Xl fa-ciiilirvuiiic 

 (j(i'loj)iic cavities have now ('xteiided so iniicli thai llicv ar<' no Jouter 

 recogiiizahle a.s \'esicles in a sin'faee view. I'iu's. oo-of) (I'h ^'I.) 

 ai'e tlirce sections from (liHci'cnt parts of" llu' ])()stci'inr ainnit)tic 

 tiil)e (ti this emljrxo. 1' ii^s. ').") lieini!' near the jxisteriol" openini:' and 

 others ijcino- in trout of it, Huh \]\c c])il)hist and somatic ]iies<;h]ast 

 ai'e re{)resented in tlicse hüuix's. the i(cIoui. the s])hinciinic niesolihi>t 

 and yolk licini:' left out, as a comparison willi Fii;'». .")0 iind iO (I'l. 

 \ .) \\ill show, Fiu'. .")(! is the median ]>ai't ol" the auinion from o\(;r 

 the middle re,Lii<)n (jf the body of the emljrv«' :njd shows the 2"reîitest 

 encroaehment at this stiige of the extni-endjryonic co'loniie cavities, 

 reducini:' the sero-amniotic connection to a meiv sej»tum-]ike ])artition, 



rigs. 21 a, h, c, and d. (IM. III.) she)w the [)osferior amniotic 

 tuhe of foui- embrvos of the staii'e a little older than that i;-i\en in 

 Tig. '24. hi a the tube is still straight, in h it is slightly c^r^('d, 

 and in r and il more curved. hi a the embi-yo is (! mm. h»i)g, while 

 tlie ])osterior amniotic tulie is only o -g mm. As this is no doubt the 

 stage of the highest development of the tube, it follows that the 

 ])ostei-ior tube in Trionyx is not as long relatively to the l)ody of 

 the embry« > as i t is in C 1 e m m y s . 



In f'igs. 'J'J (I and h (PI, Iir,) tlie posterior amniotic tube is 

 becomijjg very irregularly cur\ed. 



Iji Fig. 27 (PI. I\'.). most of the jiosterior amniotic tube has 

 already disappeared or at least is unrecognizaljle. The ])roximal or 

 basal part of it is, however, veiy distinct. At this stage, the sero- 

 amniolic connection exists from the neck-region to the tij) of the 

 renmant of the ])osterior amniotic tube. 



The maiuier in which tlie proamnion coiisisting oidy of the 

 epiblast and hy|)oblast is graduallv ri'])laced bv the amnion consisting 

 ol the e))i1jlast and mesoblast is exactlv as in Cleminys. 



