346 THE PINEAL ORGAN 



small lancet-shaped scales ; on the dorsal aspect of the head there is in 

 the centre a well-defined median pineal plate perforated by a pineal 

 foramen. The pineal plate lies between the orbital cavities, which are 

 surrounded by a ring of orbital plates ; and in front is a single — naso- 



inh.s. 

 oc.tent. v iiUijuLmJ 



^ tr. sc 



S^-tr.sc. 



B 



Fig. 243. — The Eyes of Cardium nuticum. 

 A — tentacles bearing eyes around siphonal opening. 



B — section through eye, showing the relations of the lens, retina, rods, " choroid," 

 non-cellular tapetum, and pigment layers. 1, 2, 3, 4, 5 : stages in the develop- 

 ment of the eyes. 

 c. : cornea. 

 ch. : " choroid." 

 ep. inv. : epithelial invagination. 

 inh. s. : inhalant siphon. 

 /. : lens. 

 op. n. : optic nerve. 



(After Kishinouye.) 

 The structure and development of these eyes resemble in certain respects 

 that of the lateral eyes of vertebrates. 



hypophyseal — opening similar to that in Kaieraspis auchenaspidoides 

 (Fig. 228). Moreover, behind the pineal plate there is an elongated oval 

 area marked by small scales and corresponding to the glabellar plate or 

 post-pineal area of Auchenaspis verrucosus. The Anaspida show no traces 



pig. : pigment. 



rd. : rods. 



ret. : retina. 



tap. : tapetum. 



tr. sc. : triangular screen. 



