THE GEPHYREA. 



217 



is surrounded by a circular band of cilia placed immediately 

 behind the mouth ( TFJ IF), and resembles a Rotifer or a meso- 

 trochal Annelidan larva. As development advances it loses 



Fig. 56. — Sipunculm nudus (after Keferstein and Ehlers). 1 



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; ce, oesophagus ; i, intestine; a, anus ; J, «/', loops of the intestine ; 

 x, y, appendages of the rectum ; z, fusiform muscle ; w, ciliated groove on ihe 

 inner side of the intestine ; q, anal muscles ; s, csecal glands ; t, caeca which open 

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

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

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

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



II. A larval Sipunculus about T \ of an inch long: o, mouth; «, gullet ; s, csecal 

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

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

 t, t, so-called testes ; W, W, 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, which arches over the mouth. In this state the embryo 



i " Zoologische Beitrage," 1861. 



10 



