Into the stomach, or into the adjacent portions of the digestive tract, open the ducts which connect with the so-called _liver_. The functions of this important organ have not yet been thoroughly worked out. The liver is a lobe-shaped gland of a brown-gray or light red colour, which in the spirally-shelled families usually occupies the greater part of the spire. In the Cephalopoda, the two ducts of the liver are covered by appendages which are usually known as the pancreatic coeca; the biliary duct, instead of leading directly into the stomach, passes into a very large coecum (see Fig. 144) or expansion of the same, which serves as a reservoir for the biliary secretions. At the point of connexion between the coecum and stomach is found a valve, which opens for the issue of the biliary products into the stomach, but closes against the entry of food into the coecum. In most Gasteropoda the liver consists of two distinct lobes, between which are embedded the stomach and part of the intestine. In many Nudibranchiata the liver becomes ‘diffused’ or broken up into a number of small diverticula or glands connecting with the stomach and intestine. The so-called cerata or dorsal lobes in the Aeolididae are in effect an external liver, the removal of which to the outside of the body gives the creature additional stomach-room. =The Hyaline Stylet.=--In the great majority of bivalves the intestine is provided with a blind sac, or coecum of varying length. Within this is usually lodged a long cylindrical body known as the _hyaline_ or _crystalline stylet_. In a well-developed _Mytilus edulis_ it is over an inch in length, and in _Mya arenaria_ between two and three inches. The bladder-like skin of the stylet, as well as its gelatinoid substance, are perfectly transparent. In the Unionidae there is no blind sac, and the stylet, when present, is in the intestine itself. It is said to be present or absent indifferently in certain species. The actual function performed by the hyaline stylet is at present a matter of conjecture. Haseloff’s experiments on _Mytilus edulis_ tend to confirm the suggestion of Möbius, that the structure represents a reserve of food material, not specially secreted, but a chemical modification of surplus food. He found that under natural conditions it was constantly present, but that specimens which were starved lost it in a few days, the more complete the starvation the more thorough being the loss; it reappeared when they were fed again. Schulze, on the other hand, believes that it serves, in combination with mucus secreted by the stomach, to protect the intestine against laceration by sharp particles introduced with the food. W. Clark found that in _Pholas_ the stylet is connected with a light yellow corneous plate, and imagined therefore that it acts as a sort of spring to work the plate in order to comminute the food, the two together performing somewhat the function of a gizzard.[330]