ON THE REPRODUCTIVE SYSTEM IN THE HYDROIDA. 357 
The gonophores, though presenting manifest homological parallelism with 
the polypites, have a very different form, fitting them for the special functions 
to which they are destined. They are constructed essentially on the plan of 
a gymnophthalmic medusa, but vary greatly in the degree of completeness in 
which this plan is expressed in them. They may be primarily referred to one 
or other of two principal types, based respectively upon their greater or less 
approach to the completely formed medusa. The peculiar condition by 
which one of these types is characterized may be named “ phanerocodonic” *, 
while that which distinguishes the other may be designated as ‘“ adeloco- 
donic”’ +—conditions, however, which, it must be borne in mind, pass into one 
another by numerous gradations. 
The phanerocodonic condition is found in those gonophores whose essential 
part is a typically developed medusa (fig. 1), and which are distinguished 
by having a well-developed umbrella, provided with the wide aperture or 
“‘codonostome” + which characterizes this part of the structure in the com- 
plete medusa; the umbrella, except in one remarkable form—that presented 
by Clavatella, Hincks (fig. 3), and by Eleutheria, Quatrefages—being emi- 
nently 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 have either no umbrella (fig. 2c), or, if this be present, it is in 
an incompletely developed state, never provided with a wide open codono- 
stome, and quite incapable of acting as a locomotive organ. 
The phanerocodonic gonophores, in by far the greater number of instances, 
detach themselves, either in whole or in part, from the trophosome or gono- 
blastidium after they have attained a certain degree of maturity, and lead 
henceforth an independent existence, during which they increase in size, often 
develope new parts, and sooner or later give origin to ova or spermatozoa. 
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. That there is, however, 
no essential difference between these two forms is evident from an observation 
of Agassiz, who found the gonophores of Coryne mirabilis, Agass., in the earlier 
months of the year, detach themselves from the trophosome and swim away 
as gymnophthalmic medusz before the development in them of ova or sper- 
matozoa; while, somewhat later, he has seen the gonophores attain to sexual 
maturity without ever becoming free. 
The free phanerocodonic gonophore is in a single instance 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 diastolic movements, and locomotion is performed by 
marginal tentacles peculiarly modified for creeping over solid bodies. This 
very exceptional form has been met with only in Clavatella, whose tropho- 
some has been discovered by Hincks, and in the nearly allied Zleutheria of 
Quatrefages, whose trophosome has not yet been detected. 
While all the leading features of a gymnophthalmic medusa are thus at 
once obvious in the phanerocodonic gonophore, the adelocodonic gonophores, 
* avepos, manifest, and cwdwy, a bell, + “AdnXos, not apparent, and cwowy. 
£ Kwdwy, and oroua, a mouth. 
§ The gonophores of the Calycophoride properly come under the designation of phane- 
vocodonic, though they may never become free, and though we find them departing some- 
what from the typical form of the gymnophthalmic meduse by the non-development of 
the marginal appendages of the umbrella. 
