Sullivan. — The Winter Flounder 131 



Stage 3. (Figure 3.) The type represented in Figure 

 3 averages 5.8 mm. in length. The fish from which the 

 drawing was made was six weeks old, but, due to the 

 variation in the rate of growth and development, there 

 are found between the ages of five and seven weeks many 

 fishes that have reached this stage. The features most 

 in evidence at this time are the change in the position of 

 the eyes, the well-developed fin rays, and the upward bend 

 in the posterior part of the notochord. The left eye has 

 reached at this time what may be described as a median 

 dorsal position. About half of it can be seen from the 

 right side. The right eye has taken a position slightly 

 ventral to its former position. The upward bend in the 

 posterior part of the notochord is very marked at this 

 time. This bending of the notochord seldom begins be- 

 fore the end of the fifth week in living specimens. It has 

 been pictured in younger stages, but I think this is due 

 to the fact that the drawings were made from preserved 

 material and that living specimens were not used for 

 comparison. Unless great care is taken in the killing 

 and fixing there is a distinct tendency for the posterior 

 part of the fish to bend upwards. This is also true of 

 fishes dying in dishes or rearing cars. Knowing that the 

 notochord does eventually bend upward one might be led 

 to interpret the upward bending of the posterior part of 

 the fish as the upward bending of the notochord or at 

 least indicative of it. The caudal fin rays are now well 

 developed and the original finfold is notched just dorsal 

 to the last caudal ray. The diphycercal fin of the early 

 stages has now reached the heterocercal type. The part 

 ventral to the notch is to become the caudal fin of the 

 mature fish. Otherwise the outer line of the finfold is 

 still unbroken and the fins are not entirely differentiated. 

 The pigment distribution is shown in the figure. 



From this time on the changes simply accentuate the 

 processes already under way. After the sixth week the 

 pigment on the left side tends to diminish in intensity. 



Stage 4. (Figure 4). The fish here represented is 

 about eight weeks old. At this stage the young fishes 



