x PHYLUM ANNTJLATA 479 



animal branching (coelomic) spaces in the parenchyma, between 

 the cseca, are found to be filled with ova (o). A posterior continua- 

 tion of these spaces (u) opens either into the cloaca or independently 

 of it. There are two elongated and usually branched testes (h), 

 each of which has a vas deferens leading to a vesicula seminalis (sb) 

 which opens near the lateral margin. In the hermaphrodite 

 forms the testes are matured before the ovaries, and may have 

 ceased to be functionaLbefore the ova become ripe. 



FIG. 392. Myzostoma. Diagrammatic view of the internal organs, c, cirri ; da, branches of 

 the stomach ; ed, hind-gut ; h, testes ; klo, aperture of cloaca : m, stomach ; mo, male genital 

 aperture ; o, ovaries ; p. parapodia, with hooks and supporting rod ; ph, pharynx ; php, 

 pharyngeal tentacles ; pht, pharyngeal pouch ; sb, vesicula seminalis ; m, suckers; M, uterus; 

 wo, female genital aperture. (From Lang's Comparative Anatomy, after von Graff.) 



The development of the Myzostomida closely resembles that of 

 the Polychaeta. A trochophore larva is first formed, and this 

 becomes metamorphosed into a larva with provisional setae bearing 

 a close resemblance to that of Nereis (p. 443). 



APPENDIX II. TO THE CILETOPODA. 



CLASS ECHIURIDA. 



The Echiurida are a small group of marine worms including the 

 genera Echiurus, Thalassema, Bonellia, Pseudobonellia, Hamingia, 



