70 The Swan-Mussel and its Anatomy. 



open with a finely -pointed pair of scissors the stomach, of one 

 of these molluscs you will notice a semi-transparent body, of 

 about three inches long in a large animal, and about the thick- 

 ness of a piece of whipcord, cylindrical and of the consistency 

 of jelly. M. Moquin-Tandon says that this body (called the 

 crystalline style) has been found only in the Anodon and Unio, 

 and does not exist in other acephalous molluscs. 



This crystalline style I have invariably found to contain, 

 imbedded within its substance, large numbers of a very minute 

 filiform animalcule, which may be seen under the microscope to 

 shoot backwards and forwards in the gelatinous mass. I have 

 failed hitherto to make out any structure in these curious para- 

 sitic vibrioid worms. I have examined them under one of 

 Bosse's y 2 th of an inch objective, and also under Smith and 

 Beck's 2 ^th, but as I said without the revelation of any struc- 

 ture. These vibrioid animalcules, which occur so constantly in 

 Anodonta, are not found, so far as my observations have 

 extended, in the crystalline style of Unio margaritifera or in 

 that of U. pictorum. 



The intestine of the Anodonta is a narrow tube with thick 

 jelly-like walls, which, springing from the bottom of the sto- 

 mach, makes two or three convolutions in the substance of the 

 liver and ovaries, and then rises up to the back of the ani- 

 mal, and passing in a direct line through the ventricle of the 

 heart and under the slit in the rim of the mantle, terminates at 

 the anus. 



The organs of circulation in the fresh-water mussels con- 

 sist of a heart, composed of two triangular-shaped auricles of 

 delicate structure, and nearly transparent, and one ventricle. It 

 lies on the back portion of the animal under the hinge of the 

 shell ; its pulsations, which are not more than about seven or 

 eight in a minute, are easily seen under the pericardium : the 

 heart continues to beat for a long time after the valves have 

 been opened. A French savant states that after he had 

 placed an Anodonta in boiling water to destroy it, and to pre- 

 serve the shell, the heart actually beat eight hours afterwards ! 

 The blood is nearly colourless, and the corpuscles semi- 

 transparent ; after traversing the numerous vessels of the gills 

 it is received by the large branchial veins, from whence it is 

 conveyed to the triangular shaped auricles, which have their 

 largest side adjacent to these veins, and their smallest side in 

 communication with the auricles; thence it proceeds to the 

 ventricle, which by its contraction impels the circulating fluid 

 to the aorta and distributes it to the whole system. Under- 

 neath the heart, and extending for a considerable distance 

 along the body, is seen a curious sponge-like organ of a choco- 

 late colour, which has received the name of the " gland of Bo- 



