[136] According to Willemoes-Suhm, Terebellides strœmii is also characterised by a regular segmentation.
[137] These two rings are at first (Hatschek) not quite closed dorsally, calling to mind the early condition of the Echinoderm larvæ with a præ-oral and post-oral ciliated area.
[138] The structure of the ventral cord in the adult requires further elucidation.
[139] For Semper’s view as to the intercalation of segments in the cephalic region, vide note on p. [333].
[140] It has been insisted by Semper (No. [355]) that certain of the anterior segments, belonging to what he regards as the head region in opposition to the trunk, become interpolated between the trunk and the head. The general evidence, founded on observations of budding, which he brings forward, cannot be discussed here. But the special instance which he cites (founded on Milne-Edwards’s (No. [347]) observations) of the interpolation of the head segments, bearing the gills, in Terebella appears to me quite unjustified from Milne-Edwards’s own statements; and is clearly shewn to be unfounded by the careful observations of Claparède on Ter. conchilega, where the segments in question are demonstrated to be present from the first.
[141] For further details, vide general chapter on Nervous System.
[142] Reproduction by budding and formation of the sexual products to some extent overlap.