82 



MORPHOLOGY. 



Fig. 36. 



Medusa, probably young Lizzia, captured in the open 

 3a, with luedusa-buds springing from the base of the 

 lanubiiura. 



thus traced through a series of metamorphoses into adult Gcrvonidans, it has been proved that 



certaiu other free meduscE of the /Eginidan type 

 have originated as buds from achdt forms. This, 

 however, leads us to consider the formation of hiids 

 by the medusa. 



Formation of Buch hi/ the Medum. — The 

 plienomenon of medusa-budding does not neces- 

 sarily find its extreme term in the formation of the 

 medusa itself. Many free-svviniming medasoe, some 

 of which are known to have originated in liydroid 

 trophosomes, complicate themselves by gemmation, 

 which manifests itself in the production of other 

 medusa-buds upon various parts of their bodies. 

 A fine example of this phenomenon is afforded 

 by the medusa of the tubularian hydroid, Ili/bu- 

 codon prolifer, Agass. In this beautiful animal, 

 Agassiz^ describes the base of the solitary tentacle which is continued from the distal extremity 

 of one of the radiating canals of the medusa as itself producing a cluster of medusa-buds, 

 which in time assume the form of the primary medusa, and may themselves repeat the same 

 process, through the production of successive broods of similar buds, before they become detached 

 as free natatory medusae. Steenstrup- has observed buds developed from the base of the tentacles 

 in a medusa which he believes to have originated in a Coryne-like trophosome, which he names 

 Coryne fritillaria ; Greene has described the production of buds, not only from the bulbous base 

 of the tentacles, but also along the course of the tentacles themselves in a nearly allied medusa, 

 Biplura, Greene ;' while the emission of buds by medusse has also been described by Forbes,' 

 Sars,^ Busch,^ and others. 



I have several times witnessed this phenomenon in medusae captui'cd while swimming in the 

 open sea. In some of these cases the buds were borne on the base of the manubrium (woodcut, 

 fig. 36), in others, on an elongated tubular peduncular extension of the manubrium (woodcut, 

 fig. 37), and in others upon the bulbous bases of the marginal tentacles (woodcut, fig. 38). The 

 singular ambulatory medusa of Clavatella also multiplies itself by budding from the interten- 

 tacular spaces on the umbrella-margin (see PL XVIII, fig. 5). In these various cases the buds 

 seem destined to assume the form of the medusa which save origin to them, l)ut observations on 



' Op. cit. vol. iv, p. 24"), pi. 24. 



" J. J. Steeustrup, ' Alternation of Generations,' p. 26 ; Roy. Society's Translation, 

 1845. 



^ J. R. Greene, in 'Nat. Hist. Rev.,' 1857, vol. iv. The Medusae is there named Diplonema, but 

 from this name having been already given to a genus of plants, it was subsequently changed by 

 Greene to Biplura. See my paper " Ou the Genera of the Hydroida," in 'Ann. Nat. Hist.' for INIay, 

 1801. 



* ' British Medusse.' 



^ ' Fauna lit. Norveg., erste Lieferung.' 



^ ' Beobachtungen ueber Wirbcllos. Seethieren.' 



