SPECIES ALLIED TO MOTELLA. 27 



the posterior hah' is quite black. In this specimen are seen the two spots in 

 front of the eyes which were first seen in the stage of Fig. 3, and which in 

 many cases become confluent. The number of spots on the body is now 

 reduced to twelve or fifteen, the most prominent of which are the anterior 

 and posterior pairs. 



The reduction in the amount of pigment reaches its minimum in Fig. 9, 

 twenty-four to thirty-six hours after hatching. The disposition of the pig- 

 ment-cells now plainly anticipates conditions that characterize all the later 

 stages that have come to our notice. The posterior spots, of which there 

 are here three, hold a position about midway between the vent and the 

 tip of the tail, at the upper and lower angles of the muscular myotomes. 

 In the later stages these spots multiply both above and below (more above 

 than below), forming thus two elongated patches of more or less confluent 

 cells. There is now a row of four prominent pigment-cells along the middle 

 third of the alimentary tract, on its dorsal wall. These cells also increase in 

 number, forming in later stages a continuous streak from the level of the 

 base of the pectorals to the vent. The spot on the head is small, and is des- 

 tined to disappear. In another specimen of about the same age (Fig. 8) this 

 spot is missing, or perhaps has only shifted its position to a point between 

 the eyes and a little behind them, where a single large dendritic cell is seen. 

 Five similar cells lie on the alimentary canal, and a much larger one is placed 

 at the end of the second third of the body. The eye is now entirely black. 



Fig. 12 represents a specimen twelve days after hatching, the oldest 

 stage raised from the egg. The three distinct regions of black pigment, 

 already marked out at, the stage of twenty-four hours, are here well defined. 

 The eye now shows a circle of blue around the pupil, and the head and an- 

 terior half of the body are colored with a diffuse pale brownish-yellow. The 

 termination of the alimentary canal is still far from the margin of the ventral 

 fin-fold, but it is not on this account to be assumed to be closed. 



The remaining stages were fished up from the sea, and their specific 

 identity with the young raised to the stage of Fig. 12, although not certain, 

 is quite probable, as may be seen from the character and distribution of the 

 black pigment. In the stage of Fig. 13, captured August 13, there was no 

 trace of the pale tint of Fig. 12. nor of the brighter yellow of Figs. 14 and 

 15. The ventrals were first recognized in the stage of Fig. 15 (August 31, 

 1875). A somewhat older specimen was round, duly 20, 1884, in which the 

 ventrals were longer, but entirely free from pigment. 



