Chap. II. AURELIA FLAVIDULA. 37 



water. In thi.s extreme state of extension and tenuity of tissues, tlie animal, in 

 all probability, is reduced to a degree of density corresponding to that of the 

 water, and therefore floats in a perfectly quiescent state, whether near the surface 

 or at any depth, as if it were part and parcel of the water itself The moment 

 the body contracts, as it may be made to do by touching it gently, it sinks; 

 thus affording another proof that concentration of tissues is equivalent to an increase 

 in density. Sometimes the body is only partially expanded {Figs. 20 and 27), and, 

 not being sufficiently buoyant, the oculiferous lobes (/) flap very gently, at shorter 

 or longer intervals, according as the body sinks faster or slower. Whilst swimming 

 upward or downward the upper surlace of the disk takes precedence, and is kept 

 transverse to the line of motion; but when going horizontally, the upper side of 

 the disk is tilted forward thirty or forty degrees, so that its plane rests obliquely 

 to the line which it follows. Owing to their peculiar violet color, it is sometimes 

 very difficult to detect these animals, especially in cloudy weather, when we have 

 not the advantage of the reflection of the siui from the surface of the body. 



For a while, immediately after the commencement of their wandering life, very 

 rapid changes take place in the structure of the young medusoa. In the first place 

 the whole disk expands very much, and, as we have already mentioned, forsakes 

 its concavo-convex form for a shallow double convex shape. The oculiferous lobes 

 (PI. XP. Fig. 19 j) do not lengthen, but broaden in proportion to the expansion 

 of the Ijody ; and in this state they are equal in length to the radius of the disk, 

 and, being twice as broad as the tentaculiferous edges (?'), occupy two thirds of 

 the circumference of the body. The incipient veil (/) also becomes quite promi- 

 nent, and, losing at the same time its papilla-like character and becoming flattened, 

 resembles a broad tongue. Laterally, it passes directly into the margin of the 

 oculiferous lobes (/) on each side of it. The proboscis {Fig. 19 a) does not assume 

 any new proportions, except that, in consequence of the expansion of the disk, 

 it becomes relatively smaller. "We may point out here, however, some of the 

 many protean forms which its plastic nature allows it to assume. Its natural shape, 

 when in a quiescent state, is that of a four-sided prism {Figs. 18 and 28 a a}), 

 about twice as long as thick, and having slightly concave sides. Usually the 

 corners of the mouth {<(}) project more or less sharply; and often the whole 

 circuit of the lip is curved outward {Fig. 18), thus making the proboscis trumpet- 

 shaped. At times, when in this condition, the four sides {c) collapse suddenly at 

 the upper part, and, meeting each other centrally, either close up the passage to 

 the digestive cavity, or leave only a small aperture {d). At other times we find 

 it in a similar condition, but retracted down to its very base {Fig. 14), so that, 

 with its reverted lips, it resembles a square platter turned upside down. All four 

 sides of the proboscis do not always act together, but each one occasionally seems 



