122 



THE PINEAL ORGAN 



OCELLI 



„ CORP. PEDUNCULATA 



IASMA 



Fig. 85. — Diagram showing the Connections of the Ocelli and the Facet- 

 eyes with the Brain in the Honey Bee. (After Kenyon, Jonescu, and 



FORTUYN, FROM ArIENS KAPPERS.) 



The protocerebrum of insects is connected with two optic systems, the ocelli and 

 the compound facet-eyes. Of the three ocelli the middle one is connected 

 with the pons and central corpuscle {ex.), where it acquires relations from 

 optic impressions from the compound eyes, and also with impressions from 

 the deutero-cerebrum in which the olfactory antenna ends. The corpora 

 pedunculata also receive optic impulses, but from the facet eyes only. 



The same types of larval simple and adult compound eyes are found 

 in Acilius, the large central cells of the retina, with the long rods, being 

 especially well-developed in the larval form (Fig. 82). It was this 

 example which Gaskell selected for comparison with the " pineal eye " 

 of Ammocoetes. The principal objection which was raised at the time to 

 the validity of the comparison was that the lens of the Acilius larva is 

 formed by a thickening of the cuticle, whereas in the case of the " pineal 

 eye " of Ammocoetes the lens is formed as a modification of the anterior 

 or distal wall of the vesicle and is cellular in type (Figs. 13 and 14, Chap. 3, 

 pp. 18, 19). Another objection to the theory was that the ocellus of the 

 Acilius larva was formed as a depression of the hypoderm cells, whereas the 

 " pineal eye " is an evagination from the roof of the thalamencephalon 

 after the brain has been separated from the cutaneous ectoderm. The 

 evidence in favour of and against these objections will be considered on 

 p. 358. 



It may be noted here that in the course of evolution of the inverted 



