546 



THE INVERTEBRATA 



trochosphere type. It passes into the adult by a remarkable meta- 

 morphosis which is illustrated in Fig. 407. 



Fig. 406. Fig. 407, 



Fig. 406. Phoronis. Altered from Delage and Herouard. Sagittal section 

 to show half the lophophore, the alimentary canal, one of the nephridia 

 and most of the vascular system. The middle part of the section is omitted. 

 An. anus ; aff.v. afferent and eff.v. efferent vessels ; ep. epistome ; ga. ganglion ; 

 int. intestine; Iph. lophophore; Iph.v. lophophoral vessel giving off a branch 

 to each tentacle; ne'p.a. nephridial aperture; nephr. nephrostome; n.r. nerve 

 ring; ov. ovary; org. lophophoral organ (paired); sep. septum between two 

 divisions of the coelom; st. stomach; ts. testis; ten.v. tentacular vessel. 

 Fig. 407. Actinotrocha and its metamorphosis into the adult. After various 

 authors. A, Actinotrocha larva with ciliated lobes (cil.L) and rudimentary vis- 

 ceral sac (vis.s.). B, Visceral sac evagina'ted. C, Growth of visceral sac and 

 decrease in size of preoral lobe (jpr.l.). D, Metamorphosis: mouth and anus 

 approximate, preoral lobe becomes epistome {ep.), ciliated lobes of larva 

 are seen in the mouth and new tentacles are beginning to grow. An. anus; 

 M. mouth. Alimentary canal shown by stippling, visceral sac by oblique 

 shading. 



Phoronis is very similar to a polyzoan like Plumatella but it differs 

 from such a form in the presence of a vascular system and in other 

 respects. 



