59 



is better, however, to term it simply " digestive gland, " 

 for it is evident from experiments that it secretes ferments 

 which perform functions that are specialised in separate 

 organs in higher animals. It is conspicuous both from 

 its size and its very dark colour, due to the contained 

 pigment. The gland itself is of a more solid consistency 

 than is usually the case in Molluscs. It lies dorsally to 

 the adductor muscle, against the ligament, which causes 

 a depression on its surface. 



Tlie gland completely wraps round the large 

 stomach, and there is no sign of a division into two lobes 

 in its compact mass except that the ducts open in two 

 series laterally into the stomach, as has already been 

 pointed out. 



The gland may be hxed for sectioning in Flemming, 

 Mann's Fluid or by McMunn's method, that is by placing 

 pieces of fresh gland in 20-30 per cent, formol for 12-14 

 hours, and then in 95 per cent, alcohol. 



The green pigment can be seen in ^itu whether hxed 

 in formol or by Mann's Fluid, though it is dissolved out 

 readily by spirit, if placed directly into it. 



It (fig. 50) is a tubular gland formed by the ducts 

 dividing up into numerous branches, which, ramifying 

 on their way, divide still further to form caeca. 



In Pecten this makes up practically the whole of the 

 gland, for tkere is no great development of vesicular 

 connective tissue as seen in the oyster. Moreover, in the 

 latter the secreting alveoli are to be seen in sections as 

 tubes with a, considerable cavity. In Pecten they are 

 very short, and soon become wholly solid in character, so 

 that the first diiference which one notes on comparing 

 sections of the two glands is the solidity of the one and 

 the tube-like alveoli of the other. It is difhcult to divide 

 the cells lining the ducts into different categories, for one 



