In the preceding section the mode of multiplication of the segments has already been sufficiently described[140].
Fig. 151. Larva of Phyllodoce from the ventral side. (From Alex. Agassiz.)
Apart from the formation of the segments the larval metamorphosis consists in the atrophy of the provisional ciliated rings and other provisional organs, and in the acquirement of the organs of the adult.
The great variations in the nature of the Chætopod appendages render it impossible to treat this part of the developmental history of the Chætopoda in a systematic way.
The mode of development of the appendages is not constant, so that it is difficult to draw conclusions as to the primitive form from which the existing types of appendages are derived.
In a large number of cases the primitive rudiments of the feet exhibit no indication of a division into notopodium and neuropodium; while in other instances (e.g. Terebella and Nerine, [fig. 152]) the notopodium is first developed, and subsequently the neuropodium quite independently.