150 THE PINEAL ORGAN 



types of eye which are common to the trochophore and veliger larva; of 

 widely divergent Classes of Invertebrates and the Tornaria of the Pro- 

 tochordata that we must look for the parent stem possessing a simple 



Fig. 108. 

 Frontal section through the pretrochal region of an old veliger larva of Patella 

 ccerulea, showing what are regarded as the rudiments of the cerebral ganglia, 

 eg., at the sides of the apical plate, ap. V. : velum. 

 (After Patten, from Textbook of Embroyology, Vol. 1 : Invertebrata — E. W. 



MacBride.) 



^-tent. 



sh.— 



Fig. 109. — Veliger Stage of Vermetus, a Worm-like Gasteropod which in 

 the Adult Animal is enclosed in a Tubular Shell. (After Lacaze- 

 Duthiers.) 

 In the veliger the shell is spiral and there are paired eyes and statocysts, the 

 latter being situated in the typical position behind the former. 

 cer. g. : cerebral ganglion. sh. : spiral shell. 



eye : ocellus. st. c. : statocyst. 



ft. : foot. vel. : velum. 



mo. : mouth. 



