OF THE ACALEPH^ OF NORTH AMERICA. 343 



not uniformly flat. Near the aperture of the mouth, indeed, it is smooth, and when the 

 mouth is fully exj)anded a broad funnel is opened leading directly into the digestive 

 cavity, assuming, however, in its contractions very diversified forms, being at times 

 perfectly circular, and at other times oblong, oval, or even angular. Tlie anterior 

 and posterior angles of the mouth form frequently a fold, as in Fig. 5 of Plate IV. or 

 in Fig. 2 of Plate II., and in Fig. 3, 4, 5, and 6 of Plate V. ; or it assumes a linear 

 shape, as in Fig. 7 of the same plate, or a stellate form, as in Fig. Sand 11, Plate II. 

 The more the mouth is open and spread out, the more easy it is to follow to a con- 

 siderable depth the tubes which rise vertically along the walls of the stomach, as 

 seen in Fig. 3 of Plate III., where they are slightly bent sideways to show their 

 origin from the main transverse trunk below. The walls of the stomach lower 

 down present four folds, two of which are in the direction of the fissure of the 

 mouth, along the anterior and posterior walls of the stomach, and two others at 

 right angles with them along the middle of its broader wall, in the plane of the trans- 

 verse axis of the body. These four folds are lined with brown cells, and constitute 

 probably a rudimentary liver, or at least secreting cells aiding in the process of digestion. 

 Towards the lower extremity of the digestive sac, between those prominent folds, the 

 walls of the digestive cavity are lined with a vibrating epithelium, which is particularly 

 active round the lower opening of the sac, when this is fully open. This vibrating 

 epithelium is continued upon the outer surface of the sac, and lines also, as already 

 mentioned, the inner central cavity into which the stomach thus projects. (Plate III. 

 Fig. 6 and 7.) 



If we now view this animal from the opposite side, we find a variety of organs, the 

 structure of which is not easily understood. Considering them at first chiefly in their 

 forms, it will be seen that there is an elongated area, well circumscribed in its outlines, 

 extending in a longitudinal direction in the same plane as the mouth, with a black speck 

 in its centre (Fig. 4 of Plates II., III., and IV.). Towards the centre of this area eight 

 narrow tubes are seen diverging (Fig. 4 of Plates III. and IV.), and in an oblique position 

 two indistinct projections may be observed near the margin of the area. What all these 

 parts are is not easily ascertained, and it is still more difficult to determine their con- 

 nection with other organs. The black speck in the centre (Plate V. Fig. 9 and 10) 

 rests upon a tubercle within, which is itself encircled by a tube ; but the narrow longi- 

 tudinal area is a membrane with a well-circumscribed and somewhat prominent margin, 

 covering a hollow space. The irregular transverse bulbs at the base of its anterior and 

 posterior halves, near the black speck, are the swollen extremities of two branches of 

 the medial vertical funnel. And if we start from these facts, we may perhaps throw some 



