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TEXTBOOK OP ZOOLOGY 



coelom is very much reduced due to the excessive development of the 

 mesodermal tissue. Each animal is hermaphroditic. Sperms are 

 placed on the skin of another leech, and they apparently work 

 through it into the ovaries, where fertilization occurs. Development 

 takes place in a cocoon produced by the clitellum. Two nephridia are 

 present. The nervous system is typical of the annelids. 



Fig. 113. — Glossiphonia fusca, a leech, showing annulation, segmentation, and 

 internal organs. I to XXVII, somites ; 2-70, annuli ; an, anus ; dt. ej., ductus 

 ejactulatorius ; ga and in, intestine ; ifflv, crop or stomach ; oe, esophagus ; ov, 

 ovary; po d, male aperture; po ?, female aperture; pro, proboscis; te, testes. 

 (Prom Ward and Whipple, Fresh-water Biology, published by John Wiley & Sons, 

 Inc., as modified from Castle, Bulletin of Museum of Comparative Zoology.) 



Class Gephyrea (je fi re'a, bridge). — This class is a group of 

 marine annelids which are nonsegmented, have no appendages, and 

 possess a trochophore larva. They are usually comparatively large 

 and live in shells, crevices, and such other places as will afford protec- 

 tion. In this class, the representatives of the order Echiuroidea have 

 a well-developed prostomium, used in capturing prey and in loco- 

 motion. In Bonellia, the female is the normal individual, while the 



