94 NATURAL HISTORY. OF AMIA CALVA LINN^US. 



From the above account it appears that in the male the color changes between 70 

 and 250 millimetres are three in number. The first of these is the appearance of small 

 green areas in the black or green-black of the back and sides. These areas, at first 

 indistinct, increase in distinctness and size, so that at 170 millimetres a reticular pat- 

 tern is formed by the black background remaining between the areas. The areas then 

 become larger and of regular form, and at 250 millimetres the adult reticular pattern 

 is established. The development of this pattern is possibly due to migration of 

 black chromatophores and to the consequent concentration into the reticulations 

 of the originally uniformly scattered black pigment. That such a pigment is uni- 

 formly scattered over the body in 70-millimetre larvae appears from the color changes 

 which they undergo (see p. 98). The second color change is an increase of the 

 amount of black pigments in the caudal and dorsal fins. The third change is the 

 substitution of green for the lemon and yellow color of the fins. This green, 

 together with the black of the fins, produces their normal adult color. On 

 the ventral surface of the body orange is developed in the male along with 

 green. 



The history of the larvae from 12 millimetres, when they leave the nest, to 100 

 millimetres (beyond this I have been unable to follow it) falls into two phases, that 

 during which the larvae are black, and that during which orange, lemon, and green 

 have been added to the black. In the first period the larvse are from 12 millimetres 

 to about 35 millimetres long. During the second period they are between about 

 35 and 100 millimetres long. Larvae of 30 to 40 millimetres are in transition between 

 the two periods. During the first period the larvae keep together in dense black 

 schools which are easily visible at a long distance and often seen in open water. 

 Hence larvae of this period are more often collected than older larvae. The 

 schools are closely guarded by the males, move slowly, and may be found in nearly 

 the same place when visited from day to day. The larval habit of scattering and 

 hiding when there is mechanical shock to the water is not developed until toward 

 the end of this period. During the second period the schools are found only with 

 great difficulty, since the color of the larvae is less conspicuous and they keep amongst 

 the aquatic vegetation. Often the schools may be found only by watching for the 

 bubbles of gas emitted by the larvae in their frequent trips to the surface for air. 

 During this period the schools consist of fewer individuals, which are very active. 

 The schools, consequently, are more loosely aggregated, move rapidly, and no 

 longer confine themselves to a restricted locality. The male does not guard them 

 so closely and there is less need of it. He is generally to be seen at a little distance 

 from the school, and he is much more wary than during the first period. The 



