184 PHOLADID^E. 



posterior end united to the intestine, and attached by the 

 middle to the hyaline stylet. 



This singular organ, so well known to exist, I believe, in all 

 bivalves, has caused some difference of opinion as to its use ; 

 but I think when all the incidents attached to it have been 

 mentioned, they, in conjunction with the position in the 

 stomach of the tricuspid organ, can lead to no other conclu- 

 sion than that the apparatus is a gizzard worked by the foot 

 and elastic stylet to comminute the food, and is analogous to 

 the gizzard in many of the Gasteropoda. The stylet is for the 

 basal half cylindrical, and tapers from thence to the stomach, 

 where it makes a loop, and is fixed by a filamentary muscle to 

 the gizzard or tricuspid membrane ; its colour is hyaline milk- 

 white, and in certain lights reflects the metallic hues ; the 

 working point of support is the centre of the basal part of the 

 foot, through the pedicle of which it proceeds obliquely to the 

 stomach, guarded by a sheath which appears to secrete a 

 lubricating fluid, probably having its source from the liver, 

 through the centre of which it passes to its junction with the 

 corneous attritor ; it is eminently elastic, formed of a suite of 

 circular lines ; it is impervious. I have submitted it to every 

 sectional form, but the only departure from homogeneity are 

 the fine circular elastic fibres ; in the species we now describe 

 it is fixed by a short muscle to the bottom of the foot ; in 

 P. parva it appears to rest, free. At one time I thought the 

 stylet might be the vehicle of a solvent fluid from the stomach, 

 but its impermeability negatives this idea ; and if there is a 

 connection with the foot from the stomach, it must be by the 

 sides of the walls of its sheath ; in that case a solvent would 

 neutralize the lubricity so necessary to its action, as a spring 

 for the gizzard ; besides, the most careful examination of the 

 external and internal surfaces of the foot shows no connection 

 between them, or orifice for the issue of a solvent. No ad- 

 juvant powers of sight have enabled me, in this species, to 

 discover the pore which is said to admit water to the foot of 

 many of the bivalves, or to expel it if received from the 

 jstomach. 



i now return to the intestine, which we left united to the 



