OSMEEUS MOKDAX. 37 



oi the intestine, and the remaining four, in two pairs, divide the tail into 

 thirds. The same regions are marked by diffuse bright yellow pigment, 

 which extends to the yolk-sac and different parts of the head. The eye is 

 greenish bine, with a metallic reflection. Elsewhere the fish is perfectly 

 transparent. The vent, is on the side of the fin-fold, close to the muscular 

 axis. 



The next stage ( Fig. '■'<) shows less yellow and more black pigment. The 

 distribution of the latter remains nearly the same, a single spot having been 

 added near the end of the tail. The black pigment-spots have greatly 

 increased in size. The vent has now a marginal position. A large black 

 pigment-spot is seen at the base of the pectorals, the long straight rays of 

 which spread out fan-like in the distal portion of the fin. The eye has a 

 very light greenish tinge. 



Osmerus mordax, Gill. 



Plate XVII. Figs. 4, 5. 



Two or three eggs of this species are usually found every season at 

 Newport. The egg is remarkable on account of the complete segmentation 

 of the yolk, as shown in Fig. 4. The yolk and embryo are quite transpar- 

 ent, and the yolk-segments are large and clearly defined in the living egg. 

 Sections of the hardened egg have not demonstrated the presence of nuclei 

 in these segments, and no stages thus far obtained give any clue to the time 

 or mode of their origin. The egg is somewhat oval in shape, measuring 

 .75 by .80 mm. The embryo attains a remarkable length before hatching, 

 reaching about 5 mm. ; and the yolk-sac of the newly hatched embryo is 

 many times smaller than in the stage of Fig. 4. Frontal and profile views 

 of the young fish just after leaving the membrane are seen in Figs. 5 and G. 

 Xo trace of pigment appears in the egg, nor in the young fish until it attains 

 a length of about !) mm. The stage represented in Figs. 5 and 6, and a 

 number of later stages, have been described by Agassiz* as follows: 



"The young on hatching are about 5 mm. in length, with a compara- 

 tively small yolk-sac, 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 



* Agassiz, Alexander. " Young Stages of Osseous Fishes," Part III. p. 297, Proc. Am. Acad. Arts 

 and Seieuces, XVII., 1882. 



