30 



MORPHOLOGY. 



Fig. 4. 



the greater or less approach to the completely formed medusa. The peculiar conditioQ by which 

 one of these types is characterised may be iexmeA. pJuinerocodoHic, while that which distinguishes 

 the other may be designated as adelocodonic — conditions, how- 

 ever, which, it must be liorne in mind, jjass into one another by 

 numerous gradations. 



The phanerocodonic condition is found in those gonophores 

 (PI. X, &c., and woodcut, fig. S) which present an obvious 

 medusa-form, and which are distinguished by haviqg a well- 

 developed umbrella, provided with the wide aperture, or codono- 

 donie, which characterises the complete medusa ; the umbrella, 

 except in one remarkable form — that presented by Clavatella, 

 Hincks (woodcut, fig. 5), and EhutUeria, Quatrefages — being 

 eminently contractile, and fitted for natation. The adelocodonic 

 condition is found in the bodies to which I have elsewhere given 

 the name of sporosac ; these bodies (PI. I, &c., and woodcuts, fig. 4<, 

 c, and fig. 7) have either no lunbrella, or, if this be present, it is in 

 an incompletely developed state, never provided with a wide, open 

 Group of zooids from a colony of codonostomc, and qultc incapable of acting as a locomotive organ. 



Hudraetinia echinata^ taken from near mi i i • i • i r i_i j_ 



the margin of the colony. The phauerocodonic gonopliores, in by tar the greater num- 



a. alimentary hvdrantli : hh, blasto- , p - . i i. i ^i i r ^i i i iv 



style; c, gonophores which h.we been bcr 01 mstances, dctach thcmselves iroiu the hydrosoma after 



^nc'if'fined°«tth^™\frf'ipf,i?C: they have attained a certain degree of maturity, and lead 



of'tbe' lTon?.*Vhr'a]iL*ntarrTid ^enceforth an independent e.xistence, during which they increase in 



spiral hydran'ths are ™n"ected to one J fj dcveloD ucw parts, and sooucr or later give origin to ova 



another and to the blastostyle by a ' r I ' o o 



common basal expansion or ccenosarc, q« SDCrmatOZOa 



In some cases, however, they develope and discharge their reproductive elements while still 

 attached, and then wither away, without ever becoming free, notwithstanding their well-developed 

 contractile umbrella apparently fitting them for an independent natatory existence. If an 

 observation of Agassiz be not really made on two different species instead of one, as he himself 

 believes, it would seem that this condition is dependent, in one case at least, on the season of the 

 year ; for he informs us tliat he found the gonophores of Coryne mirabilis, Agass., in the earlier 

 months of the year, detach themselves from the trophosome and swim away as gymnophthalmic 

 medusse before the development in them of ova or spermatozoa ; while, somewhat later, he has 

 seen the gonophores attain to sexual maturity, without ever becoming free.^ It is possible, 

 however, that the two conditions here described by Agassiz belong to two quite diflerent species. 



The free phanerocodonic gonophore is in one rare form (woodcut, fig. 5) ambulatory : in all 

 others it is natatory ; locomotion being effected by alternate systole and diastole of the umbrella. 

 In the ambulatory form the umbrella is incapable of evident systolic and diastohc movements, and 

 locomotion is performed by marginal tentacles peculiarly modified for creeping over solid bodies. 

 This veiy exceptional form has been met with only in Clavatella, whose trophosome has been 



^ Agassiz, ' Contributions to tlie Nat. Hist, of the United States,' vol. iv, p. 1S9. 



^ The gonophores of the siphonophorous group Cali/cophoridtB properly come under the designa- 

 tion of phanerocodonic, though they may never become free, and though we find them departing from 

 the typical form of the gynmopthalmic medusie by the non-development of the marginal appendages 

 of the umbrella. 



