DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 
797 
layers between which lies the cavity of the axial polyp. The development of the 
parts shows that this is not really the case. The upper layer alone is a direct 
continuation of the septum, while the lower layer is a secondary formation produced 
by outgrowths from the walls of the body and the septa. 
The specimen represented in fig. 207 shows an interesting abnormal condition of 
the tentacles which deserves mention. When first discovered the two lower lateral 
tentacles on the left side of the axial polyp were aborted, possessing only a single 
pair of rudimentary pinnae. The two corresponding tentacles of the first lateral hud 
on the same side were aborted in a precisely similar manner (see the figure). The 
specimen was kept alive for a fortnight, but unfortunately died before the other buds 
had acquired their tentacles. Meanwhile the aborted tentacles grew to about half the 
size of the normal ones. 
The rudimentary condition of the two corresponding tentacles in the primary and 
secondary polyps may have been due to accidental mutilation, but the chances against 
such a coincidence seem very great. If on the other hand it were due to the inheri¬ 
tance by the bud of a mutilation or monstrosity in the parent the case would be very 
interesting. 
IV.* 
GENERAL CONSIDERATIONS. 
§ 19. The systematic relations of lien ilia. 
In reviewing the development of the Renilla colony, we are naturally led to inquire 
whether the arrangement and succession of the buds throws any light on the relations 
of Renilla to other members of the Pennatulacea. Here, as in the case of the 
homologies of the organs of the individual, the basis for comparison is very narrow on 
account of the imperfect state of our knowledge. Fortunately, however, the evidence 
is enough to show how the mode of budding in Renilla may readily be reduced to the 
ordinary type as exhibited in the peuniform Pennatulids, as for instance in Pennatula 
or Pteroides. 
Kolliker was so fortunate as to obtain a very young colony of Pteioides Lacazii 
(Koll.), a representative of the typical Penniformes, and his valuable and interesting 
observations, when compared with my own on Renilla, are enough to show that the 
mode of growth is essentially the same in these widely different forms. In Pteroides 
(‘Pennatuliden,’ p. 356, plate xxiii., figs. 214, 215) as in Renilla there is a primary or 
axial polyp which produces paired lateral buds ; the order of their appearance was not 
determined nor was it ascertained whether new buds are interpolated between older 
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