Chap. II. AURELIA FLAVIDULA. 25 



shall find that m the last figure (34'') the corners of the mouth are doubled m 

 number, and each one of them is opposite an interval of the tentacles, instead of 

 being opposite a tentacle, as in the first figures ; and so we must finally come 

 to the conclusion, that the normal position of the corners of the mouth is unde- 

 terminable, if indeed there is any strict relation between them and the tentacles. 

 At other times all traces of the corners of the mouth are obliterated, and a simple 

 round opening {Figs. 25 and 32 c) leads to the digestive cavity. This is especially 

 observable when the mouth is thrown wide open (PI. X". Fig. 4 c), which may be 

 done to an extent so great that the aperture has a diameter equal to the breadth 

 of the body. Again, the mouth contracts in the form of a circle (PI. X. Fig. 3G c), 

 and, gradually lessening the aperture, it finally disappears {Fig. 30) without leaving 

 a trace of its position, just as the vacuoles in Infusoria. 



As in the previous stage, so in this, there are occasional anomalies in the regu- 

 larity of the development of the tentacles. Sometimes one of the second set of 

 four becomes far advanced in growth before the other three have scarceW begun 

 to bud {Fig. 27) ; in others, two tentacles precede the others {Figs. 29, 30, and 31). 

 In a seven-armed embryo {Fig. 32) which originally appears to have been five- 

 armed, two tentacles, one on each side of the forked one {c), precede the others. 

 A nine-armed specimen has one of the first four tentacles (PI. X\ Fig. 11 e^) 

 double from the very base. We have also figured a ten-armed specimen (PI. X'. 

 Fig. 14), which no doubt originally had five tentacles ; here every thing is in fives, 

 or multij^les of five. There are five larger (i) and five smaller {2) tentacles, 

 one of which is contracted down to a mere papilla {e), and the lips {c) are five 

 in number. These variations recall the variations in the number of segments of 

 the Medusas. The contractility of the tentacles is almost as unlimited as in the 

 youngest stages, as we have seen a well-developed, eight-armed embryo (PI. X. 

 Fig. 34) withdraw its tentacles so completely within itself that they could be recog- 

 nized only as slight protuberances {Fig. 34" e). The manner of doing this would 

 seem to be by lateral spreading and diffusion of the mass of the tentacle as it 

 sinks down into the disk, rather than by a condensation of the cells into a smaller 

 compass; for in the latter case the protuberances would be much darker than the 

 rest of the body, and the lasso-cells would be crowded together in a bristling mass, 

 which is not the fact. Sometimes, the tentacles being partially contracted, they 

 are curved inwardly toward the mouth {Fig. 36), or they may be still more con- 

 tracted, and the disk narrowed to such a degree that it is less in diameter than 

 the body below it {Fig. 34''). 



Here and there we find forked tentacles; some forking at the base (PI. X. Fig. 

 28 e), some near the tip (PI. X. Fig. 32 e; PI. X^ Fig. 14 e^), and others midway 

 between these points (PI. X. Fig. 38; PI. X^ Fig. 11 e). In PI. X. Fig. 28, the forked 



VOL. IV. 4 



