OF ARTS AND SCIENCES. 297 



FUNDULUS NIGROFASCIATUS, (7. ^ V. 



(Plates XIX. XX.) 



Sundevall has already given the principal changes of form which 

 Cyprinus undergoes while passing from its leptocardial stage to that 

 of the adult. I have traced the principal changes of growth in one of 

 our species of Fundulus, and find they agree fairly with the stages fig- 

 ured by Sundevall. That in the youngest stages the crossopterygian 

 nature of the pectorals is owing to their large size is perhaps as strik- 

 ing as in any other embryo of osseous fish known to me. (See Plate 

 XIX. figs. 5, 6, in which are given a view of the pectorals, fig. 6, 

 from above ; partly in profile, fig. 5 ; and a side view of a large 

 pectoral (fig. 4), in which the fleshy base and the embryonic rays 

 of the fin are best developed just previous to the appearance of the 

 first trace of the permanent fin rays.) The gradual change of the 

 pigment cells from a linear arrangement to the characteristic pattern 

 of the adult is readily traced in the oldest specimens figured on 

 Plate XX. 



OSMERUS MORDAX, GUI. 



(Plate XII.) 



The egg is pelagic, quite transparent ; the young on hatching are 

 about 5™°^ in length (Plate XII. figs. 1, 2), with a comparatively 

 small yolk bag, very rudimentary head, huge eyes, the vent placed 

 at about three quarters of the length of the body near the posterior 

 extremity, pectorals quite rudimentary. There are no pigment cells 

 in this stage in any of the young I have collected. In the next stage 

 figured (Plate XII. fig. 3) the young fish has greatly changed, the 

 head is quite elongate, branchiae are present, the lower jaw projecting 

 beyond the upper one, pectorals large, eye brilliant emerald green, 

 the yolk bag has completely disappeared, the caudal embryonic fin 

 rays are very marked ; we can also see the first trace of the separation 

 between the caudal, anal, and dorsal. A prominent row of large pig- 

 ment cells extends along the base of the anterior anal embryonic fin 

 fold, with a smaller line extending along the upper side of the intes- 

 tines, a few small pigment cells at the extremity of the notochord, 

 along the base of the posterior anal and of the operculum, with two 

 or three pigment cells along the dorsal line about half way from the 

 head to the tail. 



