ox THE PKOOESS OF OA^'IKULATION IX CHELOXIA. 2'dl 



to that spot some picro-sulphiiric acid, which reDiovcs calcareous 

 matter. I scrape again with the knife and again apply the acid. I 

 repeat this process, ah\ays using great care, until enough of the shell 

 is worn off to expose a very small patch of the allantoic surface, some- 

 times not larger than the eye of a needle. However small the opening- 

 may he, the acid is able to penetrate through it and harden the tissues 

 for some space around it. The opening may then be enlarged a little, 

 with perfect safety to the |)arts l)eneath. The acid is then applied 

 again, a still large area is hardened, and the opening is accordingly 

 made still larger. At length the opening becomes large enough to 

 allow of the removal of the entire shell without injury to the mem- 

 branes. In removing the shell, it is advisable to use the broad, 

 blunt-pointed forceps and insert them tangentially between the shell 

 and the fretal membranes. With a little practice, it becomes com- 

 paratively easy to obtain in this manner embryos with the foetal 

 membranes perfect, except for the yellow patch where the picro- 

 sulphuric acid was first applied. 



As to staining, imbedding, îind cutting sections, there is nothing 

 special to communicate. I generally use borax-carmine for staining. 

 For imbedding, celloidin-paraffin is used. 



The methods just described have been used in the case of Chelonia 

 caouana and in those of other species with equal success. 



Description of the stages ofGastrulation in 

 Chelonia Caouana. 



The first stage to which [ wish to call attention is represented in 

 Figs. 1 and \a. PI. VI. It was taken out of an egg which had been 

 deposited <jnly a few hours before. We notice tirst the oval -shaped 

 embryonic shield somewhat elongated in the antero-posterior direction. 

 At the posterior end of this, and for the most part, lying outside it, 



