THE CKYSTALLINE STYLE OF LAMELLIBRANCHIA. 503 



the different species of the same gi'oup of animals ; but 

 taken in conjunction with the other reasons, it must be 

 allowed to possess some value. 



(4) We invariably found in literally hundreds and hun- 

 dreds of the fresh-water mussels and other Lamellibranchs 

 that a considerable quantity of food material surrounds and 

 is embedded in that end of the crystalline style that projects 

 into the stomach (see figs. 2, 4, 6). This is very suggestive 

 to say the least. 



(5) The fact that the crystalline style is periodically 

 renewed (Claus, Sedgwick) does not fit in well with the idea 

 that it is a rudimentary structure. Why should a vestigial 

 structure be formed and vanish again and again, say once a 

 day (about that is the frequency of renewal that I found to 

 obtain amongst the mussels which I kept in an aquarium) ? 

 It rather suggests the idea that the style is somehow con- 

 nected with some important function that is performed by 

 some organ of the animal. And we have found that that is 

 the case. It is connected with the digestive function. 

 Whenever digestion is going on actively in the animal, as 

 evidenced by the presence of undigested and half digested 

 food material in the stomach and first portions of the intes- 

 tine, and of excrementitious matter in the last portion, one is 

 sure to find the style. When that function is for any reason 

 in abeyance, one fails to find it. This is shown by the 

 following observations. I used to get my supplies of mussels 

 in batches of about 200 each. After they had been taken 

 out of a pond they were kept and brought to me in a very 

 small quantity of water in a pail-like vessel. About ten 

 hours elapsed from the time they had been taken out of a 

 pond and the time they reached me. All this time their 

 position in the vessel was anything but natural. They lay in 

 the vessel like a mass of pears in a basket, — some horizon- 

 tally, some vertically, others obliquely, every one being in 

 contact with the surrounding ones. Moreover, during the 

 transit from the country to the town they had to undergo a 

 considerable amount of jostling and rubbing against one 



