SEA-FISHERIES LABORATORY. 445 
retina of such a type as is present here, the several eyes 
will have but a limited area from which rays can be 
focussed on the receptive surface. I have never observed 
the eyes of Pecten being moved im various directions, they 
ean only form an image of some object directly in front of 
them. This will account for the need of such a number 
of eyes, if they are to be of real use as visual organs, 
EXCRETORY SYSTEM. 
The most important renal excretory organs are the 
paired glands (fig. 1, A.0.) lying at the sides of the 
visceral mass, and sometimes known as nephridia. They 
were formerly termed the organs of Bojanus, after their 
discoverer, who first described them in 1819. 
Morphologically, they are like nephridia only in as 
far as they open on the one hand to the exterior and on 
the other hand into the pericardium—the remains of the 
coelom. But, since they are out-growths from the 
coelom, they are true coelomoducts. 
In Pecten, they are elongated pouches of a heht to 
dark brown colour. They are attached to the anterior 
surface of the adductor muscle, on each side of the 
visceral mass. and lie between the latter and the ctenidia, 
extending over the muscle for about 90° from the region 
of the digestive gland to near the last point of attachment 
of the visceral mass. 
They are slightly asymmetrical, the left being the 
larger of the two, and this difference is correlated with the 
position of the visceral mass. The organ lies directly on 
the adductor, the glandular walls being separated from it 
by connective tissue. The outer wall cf the organ of 
Bojanus is formed by a direct continuation of the 
epithelium of the visceral mass over it, on its way to form 
FF 
