1 62. 



ZOOLOGY 



ever, are enlarged wedge - shaped cells which almost fill up 

 the cavity of the cup. They form a secretion which passes 

 out through the narrow opening. The mouth of this is 

 protected by special horny plates, modifications of the 

 cuticle. The papillae are scattered all over the body, and 

 as they stand out from the surface, they give the animal a 

 rough appearance. 



Within the ectoderm is a layer of circularly-arranged 

 muscle fibres broken up into circular bands in the introvert. 



FiG.ip4. — The body oiPhymosoma 

 varians laid open \>y an incision 

 a little to the left of the median 

 dorsal line, so as to show the 

 internal organs. The introvert 

 is retracted. 



1. Opening of introvert. 



2. Position of brain, the two eye- 

 spots are shown. This marks 

 the level of the head. 



3. Dorsal vessel. 



4. Left dorsal retractor muscle. 



5. Left ventral retractor muscle. 



6. Generative ridge. 



7. Ventral nerve cord. 



8. Nephridia. 



9. Coiled intestine. 



10. Rectum. 



11. Spindle muscle. 



and forming a continuous sheath in the trunk ; internal to 

 this are the longitudinal muscles, continuous in the introvert, 

 but arranged in about twenty anastomosing bundles in the 

 trunk. Within this layer, the coelom is lined by flat epithelial 



