EXPLANATION OF THE PLATES. 



Plate. Fig. 



I. 1. First Stage. — Embryo of Chelone viridis, 3 J lines long/ 



,, 2. Second Stage. — Another embryo, 6 lines long, 



,, 3. Third Stage. — Embryo, 6 J lines long ; side view, . 



,, 4. Head of same ; lower view, with only two post-oral arches 



shown, and those partly cut away on one side, 

 ,, 5. Upper view of same head, ..... 

 ,, 6. A vertical section of the same, .... 

 ,, 7. Fourth Stage. — Side view of embryo, three quarters of an inch 



long, ........ 



II. 1. Head of same embryo as fig. 7 in PI. I., upper view, 

 ,, 2. The same ; lower view, ....... 13|- 



„ 3. The same ; lower view ; the object seen when tilted back 



slightly, and with the post-oral bars cut away,, . . 13|- 



The same stage ; vertical section of head, . . . . 13f 



The same stage ; head dissected from above to show cranial 



basin, .......... 13f 



Part of the same object ; fore part of basis cranii, lower view, 27-g- 

 The same ; upper view, ....... 27-j 



8. Part of fig. 7, 54f 



,, 9. Same stage ; transversely vertical section of basal region, below 



the eyeballs, ......... 41^ 



,, 10. A similar section made a little in front of the pituitary space, 27^- 

 III. 1. Fifth Stage. — Embryo, 1^ inch long; side view, 

 ,, 2. Head of same ; upper view, ..... 



1 The entire length of each embryo is given, meaeured along the ciirve, in inches and lines (or twelfths of an 

 inch). 



No. of Times 

 Magnified. 



13f diam. 



13| 



13| 



13f 

 13f 

 131 



13| 

 131 



