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. vm. New York, 

 1866. 



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

 Amer. A cad. of Arts and Scien., Vol. ix. 1873. 



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

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



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

 naria)." Zcit.fiiriuiss.Zool.,^A.Xx. 1870. 



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

 Akad., 1849 and 1850. 



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

 Naturf. Vers. Miinchen, 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-cesophageal 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. 



