50 VEEMES. 



Class I. PLATYELMINTHA. 



STERELMINTHA. SCOLECIMORPHA. COTYLIDEA. PLATODES. 



Body flat, more or less elongated, without true segments. 

 Mouth sometimes wanting. Hermaphrodite. 



These worms are of a low organization. They hare, with few 

 exceptions, no circulatory or respiratory systems, and their ner- 

 vous system consists at most of two pharyngeal ganglia giving oft 

 few branches. Some of the species are rather round than flat. 



The Scolecida of Huxley comprised that portion of his Annu- 

 loida other than Echinodermata. In the Cotylidea of Van 

 Beneden, Schmarda includes Cestoda, Trematoda, and Hirudinea. 



For Giard this class alone comprises the Vermes, and with 

 them he places Dicyema (class Dicyernida) and his genera Eho- 

 palura and Intoshia (class Orthonectida), the orders below being 

 also ranked as classes. The Orthonectida are minute, ciliated 

 animals, parasitic on Ophiuridae and Lineidas. Dicyemida are 

 parasites apparently confined to Cephalopoda. "The renal or- 

 gans of most Kepite may be said to be literally made up of these 

 organisms in all stages of growth" (Bay Lankester). According 

 to Van Beneden they are pluricellular animals, forming by them- 

 selves one of the principal divisions of the animal kingdom, 

 which he has named Mesozoa. 



With a digestive cavity. 



Cuticle ciliated ; free TURBELLARIA. 



Cuticle not ciliated ; parasitic T KEMATODA. 



Without a digestive cavity CESTODA. 



Order I. TTJEBELLAKIA. 

 PLATYELMINTHA. TERETULAKIA. 



Non-parasitic, aquatic animals, having a flattened, ovoid, or 

 elongate body, with a ciliated cuticle. Mostly hermaphrodite. 



Except in the Nemertidaj the sexes are rarely distinct. Repro- 

 duction is either by ova, by internal gemmation, or by transverse 

 fission. The intestine is either simple or branched, and in some 

 there is no circulatory system. There are eye-specks in most. 

 Some Nemertidse begin life as a helmet-shaped larva [pilidium]. 

 A peculiar proboscidiform modification of the pharynx has been 

 taken for a genital organ, for an embryo, for the digestive canal, 

 for an organ of defence, and for a parasitic worm. 



