136 WILLIAM RAY ALLEN. 



to be at least partially digested; while again much material is 

 found, even in the rectum, in perfect preservation, and often the 

 faeces themselves contain forms which are apparently unaffected. 

 Hence we may conclude that appetite fulfills its function by the 

 control of the secretion of the digestive juices, without the 

 voluntary regulation of the food supply. 



THE CRYSTALLINE STYLE. 



The literature on the lamellibranchs is particularly rich in 

 speculations concerning the function of the crystalline style; but 

 I cannot forbear adding a word here parenthetically on the sub- 

 ject, by calling attention to the excellent work done by Mitra 

 ('oi) upon it. He reviews all the previous theories and repeats 

 the experiments, extends them, and brings physiology, chemistry, 

 and comparative morphology to bear upon the matter, so that 

 there seems to be no way of escaping his conclusion that the 

 style is a digestive ferment which converts starch into sugar. 

 The previous hypothesis of Gegenbaur, that it is a secretion of 

 enteric epithelium, he holds to be true, but says that this does 

 not account for its existence. Against Balfour's notion that the 

 style is a rudiment of a radular sac he brings six weighty proofs, 

 and dismisses with two objections each the theories of Claus and 

 Sedgwick, that it is an excretion product and a reserve of nutri- 

 ment, respectively. 



In two minor particulars my observations do not agree with 

 those of Mitra. (i) In an experiment upon the renewal of the 

 style he concludes that it appears and disappears periodically. 

 But from the description of his experiment we find that the water 

 and food supply were renewed at regular intervals, whence the 

 periodicity. In a similar experiment of my own the crystalline 

 style was found to disappear only with the lack of food, and to be 

 regenerated only when food was supplied, regardless of time. 

 Then too, as long as the food supply is abundant the style is never 

 wanting. In all mussels freshly removed from the lake it was 

 found to exist. In all mussel freshly removed from the lake 

 it was found to exist. In these matters the work of Haseloff 

 ('88) also confirms my point. 



Hence the food supply must be a factor in its secretion. As it 



