ENTEROPNEUSTA. 583 



formation of the walls of the body cavity as gastric diverticula, 

 are all characters which point to a connection with Echinoderm 

 larvae. 



On the other hand the eye-spots at the end of the prae-oral 

 lobe 1 , the contractile band passing from the oesophagus to the 

 eye-spots (fig. 273), the two posterior bands of cilia, and the 

 terminal anus are all trochosphere characters. 



The persistence of the prae-oral lobe as the proboscis is 

 interesting, as tending to shew that Balanoglossus is the sur- 

 viving representative of a primitive group. 



BIBLIOGRAPHY. 



(567) A. Agassiz. "Tornaria." Ann. Lyceum Nat. Hist. vin. New York, 

 1866. 



(568) A. Agassiz. "The History of Balanoglossus and Tornaria." Mem. 

 Amer. Acad. of Arts and Scien., Vol. IX. 1873. 



(569) A. Gotte. "Entwicklungsgeschichted. Comatula Mediterranea. " Archiv 

 fiir mikr. Anat., Bd. XII., 1876, p. 641. 



(570) E. Metschnikoff. " Untersuchungen iib d. Metamorphose, etc. (Tor- 

 naria)." Zeit.furwiss. ZooL, Bd. xx. 1870. 



(571) J. Muller. " Ueb. d. Larven u. Metamor. d. Echinodermen." Berlin 

 Akad., 1849 and 1850. 



(572) J. W. Spengel. "Bau u. Entwicklung von Balanoglossus. Tagebl.d. 

 Naturf. Vers. Miinc/ien, 1877. 



1 It would be interesting to have further information about the fate of the thicken- 

 ing of epiblast in the vicinity of the eye-spots. The thickening should by rights be the 

 supra-oesophageal ganglion, and it does not seem absolutely impossible that it may give 

 rise to the dorso-median cord in the region of the collar, which constitutes, according 

 to Spengel, the main ganglion of the adult. 



