Chap. IT. AURELIA FLAVIDULA. 33 



Whilst the toiimost arid oldest disks are developing, new ones are fonning below 

 by constriction; and as these successively appear, they proceed to develop lobes 

 and sinuses like those above, until the whole scyphostoma is divided into a series 

 of superposed disks in all degrees of growth, from the ephyra (PL XI. Fig. 6 1), 

 just ready to drop off and swim away, to the slightly lobed disk {13) at the base. 

 We have observed as many as thirteen of these disks upon one scyphostoma. 

 Below this pile of disks we find another row of tentacles {Figs. 1-6 e, 11-14 e, 

 16, 17 e, and 29 f), like those at the top of the scyphostoma in its earlier stages 

 of transverse division (PI. XP. Figs. 10, 11, and 13 c). 



The development of one of the disks will illustrate the development of the 

 whole strobila. The eight lobes, which we have already pointed out in the earliest 

 ephyra, soon become pointed, or rather papillate (PI. XI. Fig. 5 2 h), and encroach 

 laterally upon the intervals. As soon as the papilla gains a definite outline, so as 

 to appear like a minute lobe or lobule on the end of the larger lobe, the latter 

 begins to assume a new form. On each side of the lobule the lobe rises gradually, 

 at first to a level with it {Fig. 10 disk 4), and at the same time the Avhole lobe grows 

 more prominent, and in consequence the intervals seem to have deepened. The 

 whole disk, in this state, resembles a low battlement. Proceeding to grow, each 

 lobe not only lengthens below the lobule {Fig. 20 / h), but, on each side of the 

 latter it projects, until in course of time two oval lappets, as long as itself, conjoin 

 to give it the appearance of a broad Y {Fig. 4, 2 h). After this, the principal 

 changes that occur in the process of development are the elongation of the lobe 

 as a whole {Figs. 6, 5, and 17, 3), a broadening of the upper part, and a length- 

 ening of the lobules. The lappets of the lobes also broaden midway, and become 

 abruptly pointed. The lobule, already twice as long as broad, becomes partially 

 hidden by the overlapping growth of the outer edge between the lappets. The 

 distance between the superposed disks gradually increases from the earhest period 

 of development, until, by the time the topmost ephyra is ready to drop from the 

 strobila, the depth of the constrictions is equal to the length of the proboscis of 

 ephyra next below {Fig. 29, 2 a). At maturity (PI. XI. Figs. I, 1; 6, i; 11, i; 

 13, i; 17, i; 24, and 29, 1) the lobes attain their greatest proportional length, and 

 the lappets (/), individually, their widest expanse. The latter have also become 

 asymmetrical, the outer edge of each, next the intervals, having assumed a more 

 decided curve than the inner one, so that, on the whole, it resembles the outlines of 

 a human foot. The lobule {h), when seen from the outside, appears to be buried 

 in the folds of the lobe between the lappets; but by looking on the inner, or, 

 homologically speaking, the lower side {Fig. 24 h), we find that it is perfectly free, 

 and that the edge of the lobe between the lappets has merely extended so as 

 to hide this lobule from exterior view. The edge of the disk, at the intervals {i) 



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