450 PRACTICAL DIRECTIONS. [APP. 



made out at this stage in the hardened specimens are 

 those connected with the visceral clefts and folds and 

 the mouth. 



If the amnion has not been removed it will be 

 necessary to pick it completely away with needles. 

 Without fui'ther pi'eparation a view of the visceral 

 folds and clefts may be obtained from the side ; but 

 u, far more instructive view is that from below, in 

 order to gain which the following method may be 

 adopted. 



Pour a small quantity of melted black wax (made 

 by mixing together lampblack and melted wax) into 

 a watch-glass, using just enough to cover the bottom 

 of the glass. While still soft make a small depression 

 in the wax with the rounded end of a pen-holder or 

 handle of a paint-brush and allow the wax to cool. 

 In the meantime cut off the head of the hardened 

 embryo by a sharp clean transverse incision carried 

 just behind the visceral clefts, transfer it to the 

 watch-glass and cover it with water or spirit. By a 

 little manipulation the head of the embryo may now 

 be shifted into the small depression in the wax, 

 and thus be made to assume any required position. 

 It should then be examined with a simple lens 

 under a strong reflected light, and a drawing made 

 of it. 



When the head is placed in the proper jjosition, 

 the following points may easily be seen. 



1. The opening of the mouth bounded below by the 

 first pair of visceral folds, and commencing to be 

 enclosed above by the now very small buds which 

 are the rudiments of the superior maxillary pro- 

 cesses. Compare Fig. 56. 



