OF THE OYSTER, MUSSEL, AND COCKLE. 13 



young are gradually expelled from the genital orifices as they 

 come to perfection. 



The generative gland of the mussel is a closely packed, racemose 

 structure, distributed chiefly between two layers of the mantle in 

 each shell, but also extending throughout all available parts of the 

 body, around the base of the foot, and the muscles of the byssus. 

 The gland thus distributed is made up of a vast number of lobules, 

 as in the case of the cockle, being also connected together in the 

 same way by stalks, using the same illustration of bunches of 

 grapes, the gland of the mussel might be roughly compared to 

 closely packed raisins, united together by a common stalk. The 

 stalk varying again with the contents of the gland, in the same 

 way as in the cockle, the tubes containing the young, however, 

 being much more limited in extent, and found chiefly among the 

 muscles of the byssus. The lobule, when filled with spermatozoa, 

 or spermatozoa and clear cells, appears as if composed of a 

 radiating and branched tubular structure, uniting in the common 

 stalk, the spermatozoa being confined to the radiating lines, the 

 clear cells being disposed between them. When the eggs are 

 present they appear to open by their micropyle into the branched 

 tubing, which ultimately unites into the common stalk. When 

 the young are hatched they are found in all stages of growth in the 

 tubular structure, and are ultimately expelled from the genital 

 orifices when sufficiently advanced. The tubular structure is much 

 like that of the cockle, being, however, much less extensive, and 

 not so muscular. 



The generative gland of the oyster is a branched structure of large 

 size, and is distributed around the liver and intestines, so that it 

 may almost be described as encasing the animal. The portion 

 which gives origin to the spermatozoa is a branched and reticulated 

 structure which forms an expanse immediately beneath the mantle, 

 sending prolongations down into the general substance of the gland. 

 When eggs are present they are found arranged in an early stage 

 around and between the prolongations of the spermatic portion of 

 the gland. At a later stage they occupy the whole gland, and may 

 be described as forming its branched structure. The eggs, instead 

 of hatching into tubes as is the case with the eggs of the cockle 

 and mussel, are extruded from the genital orifice, and, enclosed in 

 a gelatinous substance, lie in the buccal pouch, between the palpi 

 and branchial plates, until they are developed into actively moving 



