32 



the walls are very indistinct. The five retinular cells 

 contain black pigment, which Parker (16) observed to 

 migrate from the more proximal parts to the more distal 

 ones in the presence of light, and to retnrn to the proximal 

 ends in comparative darkness. He suggests that by this 

 means the more oblique rays are turned back on the 

 rhabdome in dim light, since the removal of the black 

 pigment surrounding the rhabdome exposes the whitish 

 reflecting pigment of the surrounding cells. Parker 

 believes that the pigment surrounding the cone is merely 

 concerned with the absorption of the lateral rays, oblique 

 light being prevented from reaching the underlying 

 rhabdome by the shape of the cone, which is therefore 

 catoptric in action, and is regarded by him as being in 

 many respects primitive in type. The number of 

 ommatidia increases with the age of the animal, the new 

 ones being formed at the posterior or convex margin of the 

 eye (PI. I., fig. 15). 



The Exceetory System. 



In Gammarus which had been fed upon carmine for a 

 week no granules were visible in the diverticula of the 

 gut, though the mid-gut contained a quantity of the 

 substance. Staining was observed (1) at the base of the 

 second antenna, i.e., in the antennary gland, (2) in the 

 protopodite of the second maxilla, (3) in patches just 

 below the cuticle at the base of each of the thoracic legs 

 and of the first three abdominal ones, and also on the 

 posterior margin of the last three abdominal segments. 



The antennary gland is similar to that of Gammarus 

 marinus, described by Grobben (8). It lies in the en- 

 larged basal joint of the second antenna, and consists of 

 an end-sac (PI. II., e.s.), and a convoluted tube leading 



