RICHARDS, MILLER, and HOUDE: DEVELOPMENT OF THREAD HERRING 



Figure 4. — Opisthonema oglinum larva 13.7 mm standard length. 



-- ^^^ r^-K-^^'^^v^^- ^.'rrx ^^- 



Figure 5. — Opisthonema oglinum larva 17.1 mm standard length. 



three preceding the ural centra. These three 

 centra immediately anterior to the first preural 

 were wider ventrally and had large spaces be- 

 tween the vertebral segments. At 15.5 mm, all 

 vertebral centra were partially ossified and evenly 

 spaced with narrow spaces between. In the first 

 preural and ural centra, the three rings of ossi- 



fication had widened, but the middle ring was 

 still wider ventrally than dorsally. (This asym- 

 metrical shape of the ossified rings of the verte- 

 brae associated with the caudal region obviously 

 corresponds to flexion of the notochord. The 

 ventral surface is longer after flexion than the 

 dorsal surface and, consequently, to keep the 



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