798 
DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 
ones. The young colonies of Renilla and Pteroicles are in this stage essentially alike, 
as may be seen on comparison of Kolliker’ s fig. 214 ( Pteroides) with my figs. 186 or 
187. In both, the axial polyp terminates in the median line in front and the structure 
of the colony is strictly bilateral. 
The subsequent history of the axial polyp was not followed nor has this ever 
actually been done save in Umbellularia * which is an exceedingly aberrant form, and 
may for the present be left out of consideration. Inferring its history, however, from 
a study of the adult forms, Kolliker makes the following general statement ( l.c., 
p. 420) : “ Die typische Bau dieser Stocke ist ohne Kenntniss ilirer Entwicklung nicht 
zu verstehen, und bemerke ich daher vor Allem, das der erste aus dem Embryo 
hervorgehende Polyp, den ich den Haupt, oder axial Polypen nenne, wahrscheinlich 
nicht iiberail in derselben Weise sich verhalt. Bei den Einen Forinen, wie bei den 
Veretilliden, schcint derselbe sich zu erhalten und spater, wie die secundar aus ihm 
entstandenen Individuen, einfacli als Geschlectsthier zu wirken. Bei andern Abtheil- 
ungen dagegen, wie bei den Pennatuleen, und Renillaceen, verhiimmert der axial 
Polyp schonfriih und stelltgewissermassen ein rein vegetatives Individuum dar, dessen 
Function erlischt, sobald eine gewisse Zahl secondare Einzelthiere gebildet sind. Sei 
dem wie ihm wolle, so bilden sich auf jeden Fall die spateren Einzelthiere als seitliche 
Knospen au dem ersten Polypen und beruht auf einer fortgesetzten solchen Knospen- 
bildung wesentlich die Entstehung der ganzen Colonie.” 
This statement must be slightly modified, so far as the Benillacese are concerned; 
for the axial polyp does not in this case abort but remains, as in the Veretillidce, as a 
sexual-feeding polyp (Kolliker’s statement is evidently made under the assumption 
that the exhalent zooid—“ Hauptzooid ”—is the aborted axial polyp, a view which 
has been shown to be erroneous). 
Furthermore it is not certain that the axial polyp, even in the elongated Penniformes 
and Virgulariece, remains at the anterior end, increasing in length throughout the 
growth of the colony ; for Willimoes-Suhm observed (l.c.) that in Umbellularia the 
axial polyp does not retain its original position in the median plane, but becomes bent 
to one side so as to assume a lateral position, its former place being taken by one of 
the secondary lateral buds. Still, the evidence seems to be upon the whole in favour 
of the view that the primary polyp, whether remaining functionally active or becoming 
aborted, does retain its median position in the elongated Pennatulids and forms the 
central axis of the community. 
In the simple elongated Pennatulids—as in the Bathyptilece of Kolliker —the axial 
polyp produces a series of simple lateral buds on each side, which have a bilaterally 
symmetrical arrangement, and remain simple throughout the life of the organism. 
From this condition, as Kolliker fully shows, a nearly complete series may be formed 
on the one hand through the Protoptilece, Funiculinece, Virgularince to the typical 
Penniformes, and on the other hand through the Kopliobelemnoniece to the Veretillidce. 
* Willemoes-Suhm, Ann. and Mag. of Nat. Hist., vol. xv., 1875 
