VERMES. 53 



Order 5. Mesozoa. Multicellular endoparasites of small size and 

 extremely simple structure. A ciliated ectoderm, and an endoderm of 

 one or several cells giving rise to the genital products. Sexes separate. 

 No mesoderm. Probably degenerate. Systematic position doubtful. 



Dicyemidse (Rhombozoa). A single endoderm cell. The male 

 (infusoriform embryo) top-shaped. The females either monogenic or 

 diphygenic, i.e., producing females only, or females at first and then males. 

 Dicyema (in cuttle-fishes, Octopus, Sepia). 



Orthonectidse. Endoderm of several cells, some originating 

 muscle-fibres, and others sexual products. The male elongated and 

 annulated. The female dimorphic (annulated cylindrical female, flat 

 female) and oviparous. Rhopalura Giardi, in the genital pouches of 

 the Ophiuroid Amphiura squamata. 



