OF THE ACALEPH^ OF NORTH AMERICA. 259 



They are seen In profile in Fig. 1, and appear to form a flatter arcli than in Fig. 2, owing 

 to the oblique position of tlie bulb, and the circumstance that the tentacles, with their 

 basal eje-specks, are inserted upon its prominent edges. The waving lines which are 

 observed in Fig. 2, 3, and 4, between the bulbs and outside of them, indicate the different 

 layers of muscular bundles lining the main cavity on the inner surface of the gelatinous 

 disk. Seen in profile, as in Fig. 1, they appear like vertical supports, curved somewhat 

 in the form of the letter S. The undulated outlines of the cavity in its upper part, be- 

 tween the arches of the chymiferous tubes, arise also from the undulations of the mus- 

 cular system around the bulging projection of the centre of the gelatinous mass. Fig. 3 

 and 4 both represent the same animal seen from above ; but the differences noticed in 

 the central mass arise from the circumstance, that, in Fig. 3, the main digestive cavity 

 is quite empty and contracted, and assumes there the form of a cross, with short arms, 

 from which the radiating chymiferous tubes arise above, as the tentacles of the mouth 

 arise below ; while in Fig. 4 the main digestive cavity is filled and dilated, — so much so, 

 that its prominent corners pass almost insensibly into the radiating tubes ; and what 

 gives it the appearance of a still larger organ is the circumstance, that its lateral walls 

 are covered all over with minute eggs. It was, no doubt, owing to the presence of egg 

 bunches alternating with the prominent corners of the mouth, that Mertens, in his 

 description of this genus, has characterized the central cavity or stomach, as he calls 

 it, as formed of eight distinct suckers, four larger and four smaller ones, alternating 

 with each other. But the central cavity is really square, and has only four promi- 

 nent angles, and this appearance of eight suckers arises simply from the develop- 

 ment of eggs, which are formed between the prominent angles of the main cavity, 

 upon the outer surface of its lateral walls. Moreover, these figures differ the more, 

 as in one of them, Fig. 3, the tentacles are partly retracted, and in the other, Fig. 4, 

 completely drawn in. 



I need not say, that I have found it very difficult to ascertain the true relations of all 

 these parts. Whoever will take the trouble to compare my figures with those of other 

 species of this genus will, no doubt, acknowledge that I have spared no pains in en- 

 deavouring to make out the real structure of these miimte, soft-bodied animals. As men- 

 tioned above, their slow movements, and their habit of resting quietly, suspended in an 

 immovable position in the midst of the water, have somewhat facilitated the investigation ; 

 and their habit of remaining quiet, at times, when turned upon their side, or even 

 when reversed, with the lower opening upwards, has been an additional advantage in 

 this study. I may say, that I have been successful in investigating all parts in their natural 

 relations in the living animal, with powers as high as Ocular 1, Objective 6, of Ober- 



