16 DEVELOPMENT. 



f 



end ; on the margin of these openings dark granules (marginal granules) make their appearance, 

 being the nuclei or first beginnings of the marginal fibres, which latter gradually grow forth, 

 and the stomach exhibits itself at the base of the cavity of the bell-formed disk, together 

 with the mouth and mouth-tentacle ; from the stomach vessels radiate towards the margin of 

 the disk ; — in short, the young Acalephis, being merely attached to the mother by means of 

 a short peduncle issuing from the back of the disk, develops itself in all essential organs, 

 whilst it is still attached to the mother like the bud of a plant. Finally, after a certain 

 expiration of time, it severs itself from the mother, and now swims about as an independent 

 individual. 



"I likewise found quite the same mode of perpetuation, on the 9th of May, 1837, in 

 Thaumantias multicirrata, in an Acalephis of more than one inch in diameter. In the 

 four narrow, folded together, so-called ovaries that issue from the stomach, and extend along 

 the margin of the disk, there were blossoming forth, even as described in Cyteeis, some 

 globular beU-shaped gemmules (I observed from five to six towards the external extremity of 

 the ovarium), the smallest of them furnished with four, the largest with eight black marginal 

 granules, and short marginal fibres growing forth from the former. Perpetuation by means 

 of prolification has hitherto been chiefly observed among the polypes, in which indeed it is the 

 prevalent mode, but it was latterly also observed among the Infusoria (Vorticelles), the Tunicata 

 (the compound Ascidians), and, lastly, also in some of the Annelides (the Naides and Syllis 

 prolifera, to which I may add the Filograna implexa). We now likewise recognise this 

 mode of perpetuation in an animal which will undoubtedly be declared by all classifiers to be 

 an Acalephis, against the assertion of Ehrenberg, that 'a bud-bearing or self- dividing 

 Acalephis is a contradictio in adjecto' Thus are our speculations and inferences not 

 unfrequently frustrated by a boundless and ever-varying nature." 



I am not aware of any naturalists having confirmed the observations of Sars. With very 

 great pleasure, therefore, am I able not only to bear out, by personal observation, the remark- 

 able statements of the Norwegian naturalist with respect to the species he mentions, but also 

 to extend them to other species and other genera. 



I have observed four modes of propagation by gemmation among the naked-eyed 

 Medusae. 1st. Gemmation from the ovaries, as noticed by Sars in Thaumantias multicirrata, 

 and which I have seen, though not in an advanced stage, in my Thaumantias lucida, a nearly 

 allied species. 2d. Gemmation sub-symmetrically from the peduncular stomach, as described 

 by Sars in his account of Li%%ia octopunctata. This I have seen in all its stages, exactly as 

 he narrates, in the same species, a very abundant animal in the Zetland seas. I call it sub- 

 symmetrical gemmation, for whilst the four gemmae are symmetrically arranged around the 

 peduncle, one of them is constantly in a more advanced condition of development than the 

 other three. This appears to be a generic habit, for I find the same phenomenon in Lizzia 

 blondina, a new and very distinct species of the same genus, in which gemmiparous repro- 

 duction is equally conspicuous. 3d. Gemmation irregularly from the walls of a tubular 

 proboscis. This I have discovered in a new Sarsia, which I have named Sarsia prolifera. 

 From the sides of the long peduncle many gemmules are seen springing in all states of develop- 

 ment, and presenting an indistinct spiral arrangement. There is no order of development 

 with respect to position, individuals variously advanced springing indifferently from various 

 parts of the peduncle. [See the account of the species in the Second Part.] The fourth mode of 



