No. 4.] AMPHITHOE LONGIMANA SMITH. 183 



a corresponding color. I have several times cut off parts of 

 the body to see if their color might not have been due to this 

 cause ; but whatever effect this factor may have it is certain 

 that the green color of the blood and tissues is not entirely 

 caused in this way as it may easily be observed in the isolated 

 appendages. The part played by the sexual glands in the 

 coloration of this species varies greatly owing to the variation 

 in the size of these organs. 



It is to the pigment cells that the most marked changes of 

 color are due. These cells are of two kinds, --reddish-brown 

 pigment cells, and cells with a pale green pigment. The latter 

 play an insignificant part in the coloration of the animal, as 

 they are pale in color and few in number, there being often 

 not more than a dozen on the entire surface of the body. The 

 pale green color appears most clearly in transmitted light ; in 

 reflected light they are of a silvery hue. Their size is about 

 the same as the largest cells with red pigment. Like the latter, 

 they are very richly branched, but were not seen to undergo 

 much variation in the distribution of their pigment. They are 

 mainly confined to the epirnera, being usually situated near the 

 lower margin. 



The most important elements in determining the color 

 changes are the reddish-brown pigment spots. These spots 

 are scattered all over the body and are found also on most of 

 the appendages, especially towards the proximal end. When 

 extended the pigment spots are large and very richly branched, 

 forming most beautiful objects when seen under the microscope. 

 When fully contracted these spots assume the form of round 

 dots, and all stages of expansion may be seen in different 

 specimens, or even in the same specimen, between the most 

 contracted and the most expanded state. There are a few 

 large spots near the lower edges of the epimera that are 

 generally found in an expanded condition. Even when most 

 of the spots over the surface of the body are contracted, these 

 few spots, which may be not more than a dozen on each side, 

 are usually conspicuously large. This circumstance affords a 

 convenient means of distinguishing Amphitlioc longimana at a 

 glance from other species of the same genus. 



