226 EXPLANATION OF THE PLATES. 



PLATE II. 



Fig. 1. Ovum of a goat, after Krause (Miiller's Archiv, 1837, 

 PI. I, fig. 5). 



2. Cells from the yelk-cavity of a mature hen's egg. 



3. Cells from the interior of an egg measuring a line and 



a half in diameter, taken from the ovary of a hen. 



4. Portion of the germinal membrane of a mature hen's 



egg before incubation, viewed from above. 



5. Portion of the germinal membrane from a hen's egg 



after sixteen hours' incubation. It is folded in such 

 a manner that the external surface or serous layer 

 forms the margin. 



6. Cells from the serous layer of the same germinal mem- 



brane in the neighbourhood of the area pellucida, 

 after separation of the mucous layer. 



7. Cells from the mucous layer of the same germinal 



membrane on the outside of the area pellucida. 



8 and 9. Pigment-cells of different kinds and stages of 

 development, from the tail of the tadpole. 



10. Cells from the interior of the shaft of a fully deve- 



loped wing-feather of the raven. 



11. Earlier stages of development of the same, from the 



portion of the shaft of an immature feather which 

 has not as yet become hard. 



12. Cell-nuclei, from the same, around which no cells have 



as yet formed. 



13. Flat cells splitting into fibres, from the cortex on the 



side of the shaft of a raven's feather in progress of 

 formation. 



