Chap. II. AURELIA FLAVIDULA. 21 



opposite or free eud, containing the mouth {Fig. 11 c), becomes relatively the upper 

 end of the body as regards the point of attachment; but homologically speaking 

 it is the actinal pole, and corresponds to the proboscis of the medusoid fomi. 

 By the time the embryo is fairly attached, the outer layer of transparent cells 

 has separated from the interior mass, and thus deflned itself as a distinct wall («). 

 The inner wall {!>) is in a measure distinct, but, owing to the density of the pigment 

 cells, its outlines are not very clearly defined. Occasionally there may be seen 

 spaces {(l) between the outer and inner Avails, which, as in the present instance, 

 are quite extensive, and seem to show that the two walls are very loosely con- 

 nected with each other. The nascent tentacles {e) are quite prominent. The 

 number of tentacles varies from two to three or four, but usually there are but 

 two in the beginning. At fir.st they are mere thickenings of the outer wall, and 

 appear like small, warty excrescences {e) at a short distance behind the mouth [c). 

 The cilia still show some signs of life by fitful starts, either aU together or in 

 groups at different points of the body. The mouth has not as yet any connection 

 with the digestive cavity; but a few hours later a passage is formed, and one may 

 look directly through it {Figs. 12 and 12^ c) into the centre of the body. From 

 the earliest moment of its existence as a true moutli, it exhibits all the character- 

 istic movements of later stages : the lips gape {Fig. 12 c) till the digestive cavity 

 may be looked into as if into a cup, or they open and close and stretch out 

 as if trying to seize upon something. The specimen which we have rejjresented 

 in Figs. 12 and 12" appears indistinctly five-sided when seen from above {Fig. 12*), 

 and the angles correspond to as many incipient tentacles. The ciUa, although present, 

 have ceased to vibrate, or to show any signs of vitality. The most remarkable feature 

 of this phase is the commencement of the horny sheath of the stem, which first 

 appears as a layer of transparent, amber-lUie substance {Fig. 12 /^) beneath the 

 posterior end of the embryo, and serves as a base for its attachment. The lami- 

 nated structure of the incipient sheath indicates plainly that it is a succession 

 of layers depo.sited by excretion from the po.sterior end of the body. The digestive 

 cavity occupies a large portion of the anterior 2:>art of the body, but the rest of 

 the embryo is filled by a dense, orange-yellow mass, not to be distinctly recognized 

 as an interior wall ; nor does the whole of this congregation of cells always become 



of the body has a depression, which acts like a this end of the body precedes the other parts when 



sucker, and enables the embryo to adhere to smooth the animal is swimming. Now in our Aurelia the 



bodies, or to hang pendent from the surface of depression is also at the broader end of the body, 



water. Were it not that he describes a mouth at and precedes the narrower eud when swimming ; but 



the opposite end of the body, we should be inclined we have already seen that this broad end remains 



to think that the depression he speaks of was the free, whilst it is the narrower end which becomes 



true digestive opening, especially as he says that fixed. 



