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TEXTBOOK OF ZOOLOGY 



of the oviduct. They then lie dormant and inactive in the water 

 for a period before hatching. There is considerable similarity be- 

 tween the adult rotifer and the trochophore larva of some annelids, 



Spines 



-4 



-Hooks 



. Brain 

 "Mouth 



(_ Alimentary 



canal 



_ Ventral 

 ganglion 



— Ovary 

 - Oviduct 



-Fin 



Genital 

 -pore 



■Anus 



■ Vas deferens 



Seminal 

 — vesicle 



• Testis 



Fig. 98. — Sagitta hexaptera, an arrowworm, drawn to show internal organs. (From 

 Hegner, College Zoology, published by The Macmillan Company.) 



mollusks, Nemertinea and others. This resemblance has prompted 

 the theory that the above groups are rather closely related to the 

 rotifers. 



