268 CTENOPHOR^. Part II. 



of these animals is satisfactorily made out. I shall describe their embryonic devel- 

 opment hereafter, in connection with that of Pleuroljrachia and Idyia. 



The extraordinary metamorphoses of certain Echinoderms, which the late J. Miiller 

 first observed, ought not to be neglected in connection with the study of the 

 Cteno^^hora) ; for the remarkaljle resendjlance between the singular transparent frame 

 which protects the growing embryo of some >Star-fishes and Sea-urchins and the 

 body of Ctenophorte Lobata) cannot he overlooked hy an attentive observer, while 

 the fict that the parts of that external frame present numeric combinations which 

 are unusual among Ecliinoderms, but correspond to those of the Beroid Medusce, 

 will be an inducement to institute, at some future day, a close comparison between 

 their structure. The ciliated appendages which hang downward in those larval 

 Ecliinoderms closely I'esemble the vertical rows of locomotive flappers with their 

 chymiferous tubes, as observed in Beroid Medusoe. And it is interesting to find, 

 that in Echinoderms there is a metamorphosis going on in the embryo, recalling 

 the structure of the class of Acalephs in a mamier very similar to the analogy 

 which exists between the embryos of the Acalephs and the Polyps. For whether 

 we compare the Strobila in its earliest conditions, or the young buds of Hydroids 

 from which Medusa3 arise, the analogy of these earliest states of development of 

 the Acalephs with Polyps is unmistakable ; and I have no doubt that the external 

 frame of the young Echinoderms, which Miiller has so beautifully illustrated, will 

 be found to bear the closest resemblance to the structure of the Ctenojihorte, as 

 soon as an actual comparison can be instituted with reference to the homology of 

 their structure. But it is hardly possible to make such comparisons from descriptions 

 and figures, however accurate these may be ; and Midler's attention seems not to 

 have been attracted by this remarkable resemblance, otherwise he could not have 

 failed to allude to their typical identity while describing those embryos. So much, 

 however, may already be stated, that the general arrangement of the ciliated lobes 

 of the Pluteus corresjDonds to the ambidacral rows of the Ctenophora?, and that 

 the tulies which accompany them compare closely with the chymiferous tubes of 

 the Acalephs ; Ijut notwithstanding my constant efforts in studying the embryology 

 of a numljer of Echinoderms, I have, up to this time, been able to observe the 

 growth of such species only as follow the peculiar mode of development first 

 described by Sars. 



BoLiNA viTREA Aff. is a second species, of which I have seen only a few specimens, 

 at Key West, in Florida. It is easily distinguished from Bolina alata by its more 

 elongated vertical diameter and the narrowness of the locomotive flappers. Its 

 substance is so transparent that it is difficult to follow its movements, even in the 

 clearest glass jars with the purest water ; for its ambulacra are scarcely visible as 

 grayish bands upon the sides of the spherosome, and, though iridescent, the play 



