34 SUMMARY OF CURRENT RESEARCHES RELATING TO 



variable iu number and form, in the periphery of the cell, and parallel 

 to its surface. These chromophile formations are like the vitellogenic 

 parts of certain ovocytes at the growing period. The authors give also 

 an account of the maturation and solution of the zymogen granules of 

 the glands. 



5. liamellibranchiata. 



Movements of the Shell-valves.* — F. Marceau has analysed the 

 " rocking movements " (" mouvement de bascule ") exhibited by some 

 bivalves during the opening and shutting of the shell. It cannot be 

 seen in Monomyaria, such as Perten, nor {pace Anthony) in forms like 

 the common mussel. It is well seen in Lutraria elUptim, Psammobia 

 vespprtina, Mactra glauca, Tapes decussatnx, and Venus verrucosa. It 

 is much less distinct in the freshwater mussels. The movements in 

 question are associated with the fact that the posterior adductor muscle 

 is a little longer than the anterior, and has its axis a little nearer the 

 hinge. 



Water-Currents in Bivalves.j — Hans Wallengren has studied these 

 in freshwater mussels, and also in Mytilus, Mija, and Ostrea. In the 

 resting Anodoiita, the water passes out only by the anal siphon, but 

 enters by every aperture leading to the infraln'anchial chamber. The 

 two cm-rents (ingoing and outgoing) are quite independent. In the 

 mantle cavity the water passes from the infrabranchial chamber through 

 the intertih'imentar openings to the suprabranchial chamber. The pallial 

 ciliation of the infrabranchial chamber has no importance in producing 

 the currents, nor have muscular contractions of gills or mantle folds. 

 The currents are primarily due to the lateral cilia on the branchial fila- 

 ments and to the cilia on the inner portions of the interfilamentar canals 

 and on the inner surface of the lamella. In some cases the pallial cilia 

 in the suprabranchial chamber may help, and perhaps also the marginal 

 membranelhc, but these are really filters, and the cirri on the posterior 

 margin of the filaments of Mytilus are also of some similar importance. 

 The currents in an unstimulated mussel have a constant strength, but 

 stimulation provokes iiTegularities, e.g. by closing one opening or both 

 openings. When the shell is quite shut there is still circulation of water. 

 The water in the suprabranchial chamber passes through the split-like 

 opening on the upper free margins of the ascending lamellse back into 

 the infrabranchial chamber. This communication between the two 

 chambers is also of importance when the adductor movements occur, for 

 a surplus in the upper chamber may be forced into the lower chamber. 



Ingestion in Bivalves,^ — Hans Wallengren finds that in Anodonta, 

 Mytilus, Mya, and other bivalves, the taking in of food is an active 

 process. The mouth is not always open. The food-particles are not 

 swept into the mouth by water currents, they are conducted to the buccal 

 groove and deposited there. Then the animal, if it will, may open its 

 mouth and invaginate the proximal part of the buccal groove with its 



* Comptes Rendus, cxliii. (1906) pp. 303-5. 



t Acta. Univ. Lunds, n.f. Afd. 2, Bd..i. No. 2 (1905) pp. 1-64 (3 pis., 8 figs.). 



X Op. cit.. No. 3 (1905) pp. 1-59 (1 pi., 24 figs.). 



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