230 ^'- MITSUKURI. 



can then be removed with gi'eit eise. The bhistoderni thus removed 

 was o-enerally left in a relatively hirge quantity of tlie preserving fluid 

 lor some hours longer. In more advanced embryos tlie position of 

 the blastoderm under the shell is easily told in chelonian eggs by the 

 change of colour in the shell. In all the species I have examined, a 

 white patch a]jpears in the shell over the embryo, and increases in 

 extent with the growth of the embryo, or more strictly speaking. 

 pari jiassK with the disappearance of the white over tlie embryo ; so 

 that, roughly speaking, the size of the patch is a very good indication 

 oi the size of the embryo beneath. In these stages the embryo is 

 firmly adherent t<3 the inside of the shell, with a large subgerminal 

 fluid cavity in the yolk Ijeneath it, which can be easily pierced 

 tlirougli the shell and the blastoderm with the ])oint of one blade of the 

 line scissors. liy thus piercing the cavity and cutting round just 

 inside the edo-e of the white patch through both shell and blastoderm, 

 tlie embryo is removed, firmly adhering to the cut piece ; the latter 

 can tlieii be turned o\"er, exposing the ventral surface of the embryo, 

 and the preserving fluid be poured over it, using the cut-piece as 

 a veritable Avatch-glass. After half an hour or so, the blastoderm can 

 be easily separated fr<3m the shell and placed in a larger quantity of 

 the preserving fluid. This method has the great merit of keeping 

 every part of the blastoderm stretched in its natural condition, and 

 also of milking it possible to remove a Inrge number of embryos in 

 an incredibly short space of time. 



When the embryo is very much advanced and the allantois has 

 spread itself entirely beneath the sliell, it becomes a serious (question 

 how to remove the shell without much injury to the fœtal membranes, 

 especially as the shell is leathery, and not brittle as in some 

 other reptiles. In this and similar ciises I carefully scrape tlie shell at 

 one small spot with a knife, until it becomes ((uite thin, and then apply 



