CELETOPODA 



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Hydroid Campanularia, while the sexual forms do not build 

 cases or tubes, but swim about actively in the water, and so 

 energetic are their motions that they frequently lose many of 

 their natatory bundles of bristles. The asexual stock is, there- 

 fore, a sedentary, or at times crawling worm, while the sexual 



Fig. 32. Myrianida, a marine Polychaete worm of the family Syllidse. A, the asexual 

 zooid, which produces at the posterior end the sexual zooids. B, the head of the male 

 sexual zooid. C, the head of the female sexual zooid. 



zooids are active swimming creatures. Thus we can under- 

 stand how the present condition has been derived from that 

 which occurs in other sub-families, namely, a modification of 

 the posterior segments without separation. The worms being 

 slender and delicate, the active motion of the hinder segments 

 which, as was described above, occurs in the Nereidse, caused 

 from time to time this portion of the body to break off. The 



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