26o 



SYSTEMATIC ZOOLOGY 



need not concern us here to any extent. Rhabdopleura exists 

 in the form of colonies ; it has a so-called notochord but no gill 

 slits. Cephalodiscus likewise occurs in colonies, but the indi- 

 viduals although inclosed in a common gelatinous investment 



hc>- 



FlG. 269. Rhabdopleura. A, entire zooid. a, mouth; b, anus; c, stalk of zooid; </, pro- 

 boscis ; c, intestine ; f, anterior region of trunk ; g, one of the tentacles. (After Lankes 

 B, diagrammatic longitudinal section a little to one side of the median line, 

 of proboscis; om of collar; between bt ! and V- is a diverticulum; bc s , ccelom of 



trunk; int, intestine; ;-, rectum. (After Fowler. Both A and Bfrom Parker and HasweU's 

 Text-book.) 



are not organically connected with one another; there is a struc- 

 ture corresponding to a notochord, and a single pair of gill slits. 

 Both of these animals are provided with tentacles, and as in 

 Balanoglossus the body exhibits three regions, a proboscis, a 

 collar, and a trunk. 



