48 REPORT — 1855. 



In Orcheslia, as previously observed, the absence of the olfactory denticle is 

 probably the result of altered internal conditions of the organ necessary to 

 meet the peculiar change of circumstances into air from water, in which the 

 Amphipoda normally reside. 



The denticle, when present, is situated slightly in advance of the mouth, 

 and nothing can be eaten that does not pass the ordeal of the olfactory 

 organs, for such we do not hesitate to call them. 



Taste. — The sense of the enjoyment of food, even in the highest types of 

 the animal kingdom, is not the result of the power of any especial organ. 

 The nerves which communicate the idea are developed over most of the 

 internal surface of the mouth, and it is only the consciousness of taste that 

 demonstrates their position and use. The probability from analogy is, that 

 the sensation is manifest to creatures low in the animal scale in a similar 

 manner, and is rather a faculty peculiar to the mouth in general, than the 

 result of any especial combination directed to a given part. 



In Sulcator arenarius, and only in that species, have we observed what 

 may possibly be an especial organ of taste. There is a large protuberance 

 upon the first maxilla. It has a somewhat glandular appearance, and is the 

 result of cell growth ; these cells are large and nucleated. We have failed 

 to observe the organ, or anything analogous in the same or a similar position, 

 in any of the more common and numerous forms of Amphipoda that we have 

 examined. It can scarcely be looked upon in the light of a salivary organ, 

 although its component cells possess all the characteristics of those belong- 

 ing to a secreting gland, since its position upon the maxilla, being external to 

 tlie mandibles, forbids the idea. The purpose of this organ (if it be one) 

 will require more extended and systematic observations ere it can be resolved 

 from its present enigmatical character (PI. XV. fig. 4 a). 



The Prima Via. — The oesophagus leads, as in all Crustacea, abruptly 

 from the mouth to the stomach ; it is extremely short and is directed upwards, 

 inclining rather forwards than otherwise, so that the stomach is almost 

 entirely within the cephalic ring in the Amphipoda. 



Just within the anterior opening of the stomach are two rake-like 

 organs (PI. XIX. fig. 1 a,a^; the rows of teeth form themselves on each side 

 into a convex line, the teeth being a little curved, the lower or anterior ones 

 mostly so. The apparatus directs its teeth inwards and backwards, so that 

 the food may with ease pass in, but cannot again return. 'J'lie teeth on each 

 side appear to be antagonistic sets, which probably tear and masticate the 

 food as it enters into the stomach. 



Behind this masticating apparatus there exist four simple leaf-like plates 

 fringed with long and powerful cilia, placed in pairs {hh, cc), one anteriorly 

 and the other posteriorly situated in the stomach ; immediately above the 

 second or posterior pair, apparently in a chamber of its own, is a gizzard-like 

 organ (cV). This so-called gizzard consists of several closely-packed rows 

 of fine short strong hairs, the whole formed into the shajje, vhen displayed, 

 of an inverted heart with the apex removed, and the reversed section added 

 to the base ; the walls of the cavity in which the gizzard exists is lined with 

 numerous but small hairs : the whole apparatus appears to be placed out 

 of the direct line of continuation between the oesophagus and the alimentary 

 canal. Posterior to the gizzard-like organ, there exists in some, but we are 

 not certain that it is connnon to all the Amphipoda, a long cceca or cul de 

 sac (e, e) on each side of the posterior opening of the stomach. These are 

 delicate prolongations of the wall of the stomach, and gradually become 

 narrower towards their extremity. They probably supply the stomach with 

 a gastric juice. Still more posteriorly, at the point where the stomach con- 



