THE GEPHYREA. 



217 



is surrounded by a circular band of cilia placed immediately 

 behind the mouth ( W] TF), and resembles a Rotifer or a meso- 

 trochal Annelidan larva. As developuient advances it loses 



Fig. 5Q.—Sipunculus nudus (after Keferstein and Ehlers).^ 



I. The animal laid open longitudinally — | n. s. T, tentacles; r, the four retractor 

 muscles of the proboscis; r, the points at which they were*attached to the walls 

 of the body ; te, oesophagus ; i. intestine; a, anu:? ; X J\ loops of the intestine ; 

 «, y, appendages of the rectum; 2, fusiform muscle; w, ciliated groove on the 

 inner side of the intestine ; g, anal muscles ; s, csecal glands ; t. cseca which open 

 on each side of the nervous cord, and are gonerally considered to be testes ; p, 

 pore at the hinder end of the body; ??, nervous cord, which ends in a Inbed gan- 

 glionic mass, close to the mouth, and presents an enlargement, g\ at its poste- 

 rior end ; wi, m', m". muscles associated with the nervous cords. 



II, A larval Sipunculus about rV of an inch long: 0, mouth ; ce, gnllet ; 8, csecal 

 gland; t. intestine with masses of fatty cells ; a, anus ; w, ciliated groove of the 

 intestine ; g. brain with two pairs of red eye-spots ; », nervous cord, p, pore; 

 t, t, so-called testes ; TF, TF, circlet of cilia. 



this apparatus, and passes gradually into the adult form. In 

 PJioronis, the embryo is also mesotrochal, but it has two 

 ciliated bands, one circular, round the anus, and the other im- 

 mediately behind the mouth. The post-oral band of cilia is 

 produced into numerous tentaculiform lobes, and fringes the 

 free edge of a broad concave lobe of the dorsal side of the 

 body, vvhich arches over the mouth. In this state the embrj^o 



1 " 



Zoologische Beitrage," 1861. 



10 



