458 PBAGTICAL DIRECTIONS. [APP. 



VIII. Examination of the process of Segmentation. 



To observe the process of segmentation it will be 

 found necessary to kill a number of hens -which are 

 laying regularly. The best hens lay once every 24 

 hours, and by observing the time they usually lay (and 

 they generally lay pretty regularly about the same 

 time), a fair guess may be made beforehand as to 

 the time the egg has been in the oviduct. By this 

 means a series of eggs at the various stages of seg- 

 mentation may usually be obtained without a great 

 unnecessary sacrifice of hens. For making sections, 

 the yolk must in all cases be hardened as a whole, 

 which may be done as recommended in VI. G. 

 Chromic acid is an excellent reagent for this and 

 it will be found very easy to make good sections. 



In the sections especial attention should be paid, 



1 To the first appearance of nuclei in the segments, 

 and their character. 



2. To the appearance of the horizontal furrows. 



3. As to whether new segments continue to be formed 

 outside the limits of the germinal disc, or whether 

 the fresh segmentation merely concerns the already 

 formed segments. 



4. In the later stages, to the smaller central and 

 larger peripheral segments, both containing nuclei. 



For surface views, the germinal disc, either 

 fresh or after it has been hardened, can be used. 

 In both cases it should be examined by a strong 

 reflected light. The chief point to be noticed is 

 the more rapid segmentation of the central than of 

 the peripheral spheres. 



