THE MEDUSiE. 17 



though these animals, whose remarkable origin we have 

 just traced, must be considered as Medusa, still they 

 will be foimd to differ in many respects from the Medusce 

 whose offspring they are, (vid. figs. 29 and 25), especially 

 in the form of the border of the disc and of the prehen- 

 sile tentacles or marginal filaments attached to it ; in the 

 extent of the vessels of the disc, and in the shape of the 

 stomach. But on continuing to observe their growth, 

 we in a short time witness the disappearance of these 

 differences as they approach nearer and nearer to the 

 form and relations of the full-grown animal (figs. 25 — 30.) 

 Dm'ing their growth, for instance, the eight segments or 

 separate lobes of the margin increase but very little in 

 size, whilst on the contrary the intervals between them 

 enlarge very much, and thus the lobes or segments be- 

 come gradually much depressed (fig. 29.) In the fissures 

 of the lobes, exactly at the point where the ocelli, as they 

 have been termed, or colom^ed specks are placed, as well 

 as in the middle of the interspaces between the lobes, 

 are seen, proceeding like rays from the middle of the disc, 

 canals, or vessels, which are connected with each other 

 towards the border of the disc by a set of circular or 

 annular vessels, arranged in small arches which ascend- 

 ing slightly from the extremities of the radiating canals 

 proceeding to the interspaces of the lobes towards 

 those going to the edge of the body form segments 

 of circles, smaller in proportion to the less size or age of 

 the animal (vid. figs. 27, 38, 29, and 31, 32, 33.) As 

 the arches and interspaces alter, certain organs begin to 

 appear on the external side of each arch, between it and 

 the edge of the disc. The formation of these organs 

 commences with the appearance of a vesicle with opaque 

 contents, at the middle of the arch, and similar vesicles 

 are afterwards formed successively on the sides of the 

 first one. 



As the nmnber of these vesicles increases, those first 

 formed become larger and gradually project from the 

 substance of the disc, at first as short protuberances and 



2 



