GENERAL ZOOLOGY 



Brain 



Pharynx -<1^ 



Reproductive 

 complex 



Marginal eyes 

 Frontal eyes 



Tentacle 



Cerebral eyes 



Uterus 

 (oviduct) 



Sperm duct 



Spermiducal 

 vesicle 



Female 

 gonopore 



Fig. 11.11. Order Poly- 

 cladida. .-1, a typical poly- 

 clad, Plarwcera graffi. B, 

 composite diagram showing 

 general features of polyclads. 

 {A, redrawn, after A. Lange, 

 from E. Bresslau in W. 

 Kiikenthal and T. Krum- 

 bach, 1933, Handbuch der 

 ^oologie: B, redrawn from L. 

 H. Hyman in F. A. Brown, 

 Jr., el al.. Selected Invertebrate 

 Types, copyright 1950 by 

 John Wiley and Sons, Inc., 

 printed by permission.) 



Mesostoma, but in most species the mouth is anterior. The brain Hes dorsally, 

 and from it the two principal nerve cords extend posteriorly in the ventral 

 part of the body. The make-up and position of the nervous system in the 

 forms with an anterior mouth are similar to those of the nervous systems in 

 other invertebrates. The chief features are a dorsal brain, circumenteric 

 connectives, and a pair of ventral nerve cords which may be separate or fused 

 at the midventral line. Some rhabdocoels reproduce activelv by fission, form- 

 ing chains of individuals which remain together for a considerable time before 

 they separate (Fig. 11.10). 



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