342 THE PINEAL ORGAN 



they course distally, acquires an enamel-like appearance. This agrees 

 very closely with the enamel which occurs in the true fishes. Beneath the 

 superficial layer are pulp-like cavities, from which radiating " dentinal 

 canals " issue. From its minute structure Stensio concludes that the 



i/i Apis. A fossil bee, 

 2/1 after Maye. Fossil 



A B 



Fig. 239. 



A — Xylocopa senilis. Miocene. Baden. (After Heer.) 



snowing ocelli and lateral compound eyes. 

 B — Prionomyrmex longiceps. Oligocene, Baltic amber. 



ant, showing ocelli and compound eyes. 



(From von Zittel.) 



exoskeleton with the exception of the most superficial part of the super- 

 ficial layer which was formed by the epidermis must have arisen in the 

 corium, and also that it occupied the corium in its entire thickness. In 



A B 



Fig. 240. 



A — Aracheoniscns Brodei. Purbeck, Wiltshire. A small fossil crustacean similar 

 in type to the wood lice of the living species. (After Woodward.) 



B — Eosphaeroma Brougniarti. Middle Oligocene, Butte de Chaumont, near Paris. 

 (After Quensted.) Order Edriophthalmia. Sub-order Isopoda. Both 

 specimens show large sessile eyes on the sides of the head. 

 (From von Zittel.) 



Thyestes verrucosus, the superficial layer is incomplete, and is limited to 

 the tubercles, the middle layer being exposed in the inter-areal grooves. 



Beside the exoskeleton there was beneath it a continuous bony endo- 

 skeleton, in which was lodged the brain, sense-organs, cranial nerves and 

 vessels, and the branchial system ; and Stensio considers that it is probable 



