98 



THE PLANARIAN 



union; several zygotes, surrounded by thousands of yolk cells which 

 serve as food, are enclosed in small capsules which are attached by 

 stalks to the under surfaces of submerged objects. Spherical embryos 

 are formed and these become transformed into the miniature worms, 



mouih — 



gut — 

 v'eaicle, ---'' 



.seminal /'' 

 receptacle 



yoiH glands 



^esiis — 



mucker. 



A 



hook 



— —pharynx '' 



— oen'ital (xtrium 



■ -contractile. bia<Afer 

 --egg in ui&ru^ 



" - ovary 

 -yolk duct 



— testis 



— yolk y/anc/i 



a ^^ 



'Ss>) Alir> shell ^IdnJ 



Fig. 48. — SpMjranura osleri, a monogenetic trematode parasitic on the am- 

 phibian Necturus. A, ventral view to show internal structure. B, section of 

 surface membrane, with tactile structures. C, small hooks, which occur 

 lateral to the suckers and are surrounded by chitinous rings at the point of 

 projection from the surface membrane. D, digestive system. E, nervous 

 system. F, median, longitudinal section of anterior end. 



(Redrawn from H. R. Wriglit and A. B. Macaltum, 1887, Jour, of Morphology, vol. 1.) 



or juveniles, which hatch from the capsules. The capsules may be 

 collected as laid by worms in laboratory cultures or in nature, and the 

 later embryonic stages obtained by dissection from such capsules; 

 the earlier stages can be effectively studied only in sections. Repro- 



