Chap. II. AURELIA FLAVIDULA. 17 



for instance, the inner wall {Fig. 33 h) expands inward until the digestive cavity 

 {cl) is nearly or entirely obliterated for the time being. 



In the next phase the body assumes an ovate form {Fig. 34), with the mouth 

 {c) at the broader end. From this it soon passes into an elongate pyriform or 

 broadly cylindric shape {Fig. 35), at the same time increasing to nearly double the 

 size, but the different regions of the body retaining the same relative proportions. 

 Soon, however, more decided changes occur, and the embryo pursues a more varied 

 and active life. In the first place the body becomes slightly flattened, or four- 

 sided, at the upper half next the mouth {Fig. 36 c), and the four corners (e) project 

 slightly, whilst at the opposite end (c^) the body assumes a narrower and truncate 

 form; so that, on the whole, the body appears wedge-shaped in outline. The outer 

 wall («) retains the same thickness as in the last phases, but the inner wall {b) 

 grows thin at the four corners (e) of the actinal end, and the digestive cavity 

 {d) embraces twofold the extent that it did in the last stage, and in some cases, 

 when the embryo is unusually large {Fig. 36), fourfold. The average length of 

 the body at this time is yJ-Q of an inch, but there are here and there some 

 embryos which measure ^L of an inch long {Fig. 36). In the latter case it is 

 proljable that the embryo is very much expanded. The vibratile cilia are no 

 longer than at the earliest periods; and, as a natural consequence, the movements 

 of the embryo are heavy and slow to vary, and the onward motion is very tardy 

 in comparison with that of the embryo of Cyanea (PI. X. Figs. 10 and 10''). The 

 rosy hue of the former phases has deepened to a brownish pink color, which 

 lines the whole digestive cavity and renders it very conspicuous. This phase is 

 the last one in the free life of the scyphostoma of Aurelia, and in the next we 

 find the embryo settling down upon the narrower end of the Isody and attaching 

 itself to its foundation by a horny secretion. 



After this phase the mode of development, and the proportions and size, of 

 the scyphostoma of Aurelia and Cyanea, are to all appearance identical; and we 

 shall therefore describe them together, as if they Avere one, after having described 

 the earher stages of Cyanea, corresponding to those of Aurelia already considered. 



The Egg of Cyanea arctica. We have observed only two stages in the develop- 

 ment of the egg of Cyanea; one at quite an early period, and the other at 

 maturity. It is proper to state here, that the eggs may not have been in a perfectly 

 natural condition, as the animal from which they were taken was in a dying state. 

 The first (PI. X. Fig. 1) of these two stages corresponds in size to Fig. 19, PI. X\; 

 but the latter is in a much earlier state of development. The magnifying power 

 used here was about four hundred diameters. The yolk sac is very thin, and 

 appears like a mere film around the yolk. The yolk is very transparent and 

 colorless, and consists of rather coarse granules, not very closely crowded except 



VOL. IT. 3 



