OP ARTS AND SCIENCES. 



75 



so far removed from the bony fishes as has been supposed. On the 

 contrary, it approaches them not only by the development of the gen- 

 eral features characterizing the posterior extremity, by the mode of 

 formation of the unpaired fins from the embryonic fin-fold, by the 

 mode of formation of the fin-rays, and also by that of the ventrals. 

 The pigment cells, so well developed in their young stages, before 

 the appearance of scales, are similar to those of bony fishes, with the 

 exception that we have in addition, in early stages, cells of a white 

 silvery lustre, which are undoubtedly the first trace of the enamel to 

 form the armor of the " Garpike." 



EXPLANATION OF THE PLATES. 



PLATE I. 



Fig. 1. Young Lepidosteus just escaped from the egg, measuring 8 mm - in 

 length. 



2. Tail of specimen slightly older. 



3. Tail of specimen somewhat older than fig. 2. 



4. Head of young Lepidosteus just hatched, showing the mouth cavity 

 and the disk. 



4a. The same, seen somewhat more in profile. 



5. Another specimen, with the head thrown back, looking into the mouth 

 cavity. 



6. Head seen in profile, showing the gill-arches, the heart, the auditory 

 capsule, and the muscular segment covering the chorda. 



7. In stage of fig. 1 (hatched the same day), seen from above. 



8. Head of specimen somewhat older than fig. 7. 



9. Gill-arches of specimen in stage of fig. 7. 



10. Shows position of heart in middle of anterior part of the yolk-bag. 



11. Young Lepidosteus at the end of the first day. 



PLATE II. 



12. Young Lepidosteus, seen from above, three days old. 



13. Same, seen in profile. 



14. Profile of young on the fifth day after hatching. 



15. Same as fig. 14, seen from above. 



16. Gill-openings of same specimen. 



17. Same age as fig. 14, seen from the lower side. 



18. Anterior part of young Lepidosteus, ten days old, seen from below. 



