APPENDIX VIII. 309 



ing the second and third days the furrows develop. There 

 exists ordinarily, as soon as the beginning of the second 

 day, two furrows in the form of a cross. At the end of 

 the second day the mulberry form has reached its devel- 

 opment. On the third day it is insensibly effaced, and the 

 germ becomes smooth ; but it is, however, opaque, ow- 

 ing to the cells accumulated in its interior. On the fourth 

 day the embryonic germ represents a hemisphere of granu- 

 lated appearance, but smooth on the exterior, reposing on 

 the oily disk. All the cells are perfectly developed, and 

 all have nuclei. Those of the outer stratum are even pro- 

 vided with nucleated cells. From the sixth to the ninth 

 day the epidermoidal stratum detaches itself insensibly 

 from the other embryonic cells, overruns the yolk, and the 

 embryo separates more and more from the yolk vessel. 

 At the beginning of this period the germ represents a 

 large sunken mass, which hardly passes the borders of 

 the oily disk. Finally, there is only a little space in the 

 yolk free, the yolk cavity ; all the rest is filled up with 

 the epidermoidal layer. The embryo is diametrically op- 

 posite to the yolk vesicle, and it is in correspondence with 

 its length that the cells are the most heaped up in the 

 place where the primitive bands form. On the tenth day 

 the dorsal furrow appears and takes the form of a large 

 and tolerably deep fissure, but ending indistinctly in front. 

 The cephalic extremity of the embryo is large, square, 

 and truncated. The caudal extremity is lost in a vague 

 way in the keel surrounding the yolk cavity, which grows 

 continually narrower. The dorsal part of the embryo is 

 more narrow than the two extremities. It is, besides, 

 curled in a uniform manner around the yolk, and tlie dor- 

 sal furrow is wide open ; tlie germ and the yolk vesicle are 

 diametrically opposite. On the eleventh and twelfth day 

 the dorsal furrow ends in front, and shows the first traces 

 of the enlargements which correspond to the three cere- 



