134 BKEEDING-IIABITS OF SOME WEST-AFRICAN FISHES. 



PLATE X. 



The figures of this Plate illustrate the extcrual features iu the development of Protopterua 



aiineciem, Ow. 



Fi"-. 1. Egg on the first day of observation, segmentation somewhat advanced : p. 121. 



Fig. 2. l^gg on the morning of the second day, sliowing commenceraent of invagination : p. 121. 



Fig. 3. Egg on the evening of the second day, showing a further stage of invagination. Above is 

 seen a transparent portion indicating the segmentation-cavity : p. 121. 



Fi". 3 a. A variation of the stage shown in fig. 3. The area of the disappearing yolk-cells is 

 viewed from a somewhat different aspect, in order to show that the line of invagination is 

 not here straight but curved : p. 121 . 



Fig. 4. Egg on the morning of the third day, showing the straight line of invagination and the 

 gradual disappearance of the large-celled yolk : p. 121. 



Fio'. 4 a. A variation of the stage shown in fig. 4, showing that the line of invagination is 

 not always straight : p. 121. 



Fig. 5. Egg on the evening of the third day, showing the last stage of invagination : p. 121. 



Fig. G. Egg on the morning of the fourth day, showing medullary folds encircling the blasto- 

 pore : p. 122. 



Fig. 7. Embryo on the evening of the fourth day, showing origin of optic outgrowths, mandibulo- 

 hyoid fold, branchial eminence, and pronephros : p. 122. 



Fig. 8. Embryo on the fifth day, showing the segmentation of the mandibulo-hyoid fold and 

 first segmentation of branchial eminence; also the remnant of the blastopore, and the 

 first appearance of the cement -organ, and the development of the head and tail-folds : 

 p. 122. 



Fi°'. 9. Embryo on the sixth day, showing the further segmentation of the branchial eminence 

 into four : p. 122. 



Fio-. 10. Embryo on the seventh day, showing the first pairs of external gills strongly differentiated 

 from the second, third, and fourth pairs. The trunk of the embryo has grown back 

 from the main mass of yolk, taking much of the yolk with it. The true tail is not yet 

 formed : p. 122. 



Fi"-. 11. Larva on the eighth day, just hatched, showing further growth of the external gills, and 

 the auditory sacs showing through the tissues. The true tail-region has now begun to 

 grow : p. 122. 



Fi"-. 12. Larva on the tenth day, showing the serial arrangement of the external gills, the indica- 

 tion of the spiracular cleft, the first trace of the hind limbs, being now anterior to the 

 position of the cloaca, and the well -developed and functional cement-organ. The tail-fins 

 are now well-developed. Pigment has appeared on the head : p. 123. 



Fig. 13. Larva on the seventeenth day, showing general advancement, the rotation of the external 

 gill, the operculum, the vessel in the spiral valve groove, and the well-developed limbs : 

 p. 123. 



