Chap. III. GROWTH OF CYANEA. Ill 



which may explain their rare appearance near the surface. The youngest specimen 

 of Cyanea arctica, observed by my son, was in the habit of remaining attached 

 to the bottom of the jar in which he kept it ahve for about ten days, hardly 

 ever moving unless disturbed. We are so accustomed to consider Medusa3 as 

 animals floating in the water and basking near its surface, that the explanation 

 here given of the rare occurrence of young Cyanere may appear qiiestionable, and 

 I would hardly have ventured to suggest it, had I not become acquainted with a 

 kind of Medusa, in Florida, of which I shall give an account in another chapter, 

 which is hardly ever seen at the surface of the water, at any time, even when 

 adult, but found by thousands, groping in the mud and hardly moving, crowded 

 upon one another, like barnacles upon rocks. 



Though it does not exhibit such marked changes as those noticed among the 

 tentacles, it is interesting to see how the actinostome is gradually modified during 

 its growth. In the young, the four corners of the mouth are prolonged as four 

 independent, distinct, arm-like appendages, similar to those of Pelagia or Chrysaora, 

 the middle part of which is evidently miach thicker than the mai'gins; but with 

 advancing age, the sides of each arm widen, and assume the curtain-like appearance 

 characteristic of the adult. The degree of enlai'gement of these pendant curtains 

 varies in different species, as well as with age. They are most expanded, and 

 exhibit the largest number of folds in Cyanea arctica, and least so in Cyanea 

 versicolor, while C. fulva stands intermediate between the two, in that respect. 

 These changes of the actinostome not only show the close homology between the 

 so-called arms of the Aurelia and the pendant curtains of the Cyanea, but also 

 the relative standing of the different genera of Discophorae which are most nearly 

 allied to Cyanea. For it is plain that Pelagia and Chrysaora, in which the acti- 

 nostome retains, through life, the structure it has in the young Cyanea, must be 

 inferior to Cyanea itself, and the changes which the horizontal part of the lower 

 floor undergoes, confirm this inference. In the youngest Cyanea observed thus far, 

 the pouches, radiating from the central cavity towards the peri23hery, were defined 

 merely by the attachment of the lower floor to the upper floor, along the long 

 and short junctions; but no traces of concentric or radiating folds were observed. 

 When, however, these folds make their appearance, they are comparatively few, 

 occupying narrow bands, which go on widening and enlarging with age, and with 

 their development the number of tentacles increases I'egularly. In these features, 

 again, we find an agreement between the young Cyanea and the genera Pelagia 

 and Chrysaora, and also a coincidence with the genera of the family of Cyaneidae 

 proper, which rank below Cyanea, such as Stenoptycha. 



In a morphological point of view, the changes of the ocular lobes are also 

 highly instructive. In the young Cyanea, they resemble very much the oculiferous 



