THE STRUCTURE AND AFFINITIES OF SACCOCTRRUS. 415 



and the sides of the oesophagus (figs. 17, 18, and 19), below 

 which they join to form a complete loop just behind the 

 muscular pharyngeal sac (figs. 20 and 2). A few nuclei, 

 especially in this region, indicate the presence of ganglionic 

 cells. Obviously this loop represents the stomatogastric 

 system.^ 



A small knob with sensory hairs is situated behind each 

 parapodium. 



Alimentary Canal. — Hitherto the alimentary canal of 

 Saccocirrus has been described as quite simple, without 

 special muscular phai'ynx. In my specimens, however, I 

 find a well-developed muscular pharyngeal sac below the 

 oesophagus," opening forwards into the buccal cavity (figs. 

 1 and 2), and extending backwards into the third segment. 

 The roof of this diverticulum is thin, and the floor is 

 thickened into a sort of muscular pad (figs. 1, 19, and 20). 

 Special muscles, passing from the hinder lip of the mouth 

 backwards round the sac, and then forwards to be attached 

 dorsally to the Aval I of the oesophagus, serve no doubt to 

 push the sac and its pad forwards and outwards; but I have 

 never seen this apparatus in action. 



The inside of the sac is lined with rather thick cuticle, and 

 is not ciliated like the rest of the digestive tract. Behind 

 this organ is the glandular region with muscular walls, repre- 

 senting the digestive stomach. It reaches, as already de- 

 scribed by Marion and Bobretzky, to about the fourteenth seg- 

 ment. Following on this is the long sacculated intestine, the 

 absorptive region, covered externally with chloragogen cells. 



Vascular System. — Of the blood-vascular system, 

 Marion and Bobretzky only found the dorsal vessel ; Frai- 

 pont figured a ventral vessel (3). Langerhans had previously 

 described this ventral vessel, and a vessel passing into the 



' Surely it is lo sucli a stomatogastric system that the subcesophageal 

 ganglion of Rotifers is to be compared, and not to the ventral nerve-cords of 

 the body-wall as urged by Eisig (" Zur Eatwicklungsgeschiolite der Capitel- 

 liden," 'Mitlh. Zool. Srat. Neapel,' vol. xiii, 1898). 



' Jhe sac is f^bsent in two out of a dozen series of sections. 



