PHYLUM ANMl^LATA 



491 



are united in most cases, separate in some. In the hermaphrodite 

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

 ceased to be functional before the ova become ripe. 



The development of the Mj^zostomida closely resembles that of 

 the Polycha^ta. A trochophore larva is first formed, and this 



Flo. 385.— layzostoma. Diagrammatic view nf tlie internal organs, c, cirri ; da, branches of 

 the stomach ; erf, hind-gut ; h, testes ; klo, aperture of cloaca ; ttt, stomach ; luo, male genital 

 aperture ; o, ovaries ; p, parapodia, with hooks and supporting rod ; ph, pharynx ; ji/tj?, 

 pharyngeal tentacles ; p/tt, pharyngeal pouch ; sb, vesicula seminalis ; u, uterus ; ico, female 

 genital aperture. (From Lang's Camparatiie Anatomy/, after von Gr.aff.) 



becomes metamorphosed into a larva with jDrovisional set;e bearing 

 a close resemblance to that of Nereis (p. 451). 



CLASS IT.— GEPHYREA. 



The Gephyrea are marine Annulata devoid of any trace of segmen- 

 tation in the adult condition, without parapodia, and either without 

 setae or with only a limited number ; with either an invaginable 

 anterior body region or introvert, at the extremity of which is the 

 mouth surrounded by tentacles, or with a long, highly retractile 

 proboscis representing the pre-oral lobe of the larva, and having 



