40 Journal of Comparative Neurology. 



tween the pigmented cells others are imbedded which can be 

 compared to the rods of the visual cells in the paired eyes of 

 vertebrates and which appear connected below with nerve fibres. 

 It remains undecided whether the organ serves for sight or the 

 perception of warmth. It is also undecided whether the organ 

 is a structure developed as a special modification of the epiphy- 

 sis of reptiles alone, like for example, the development of the 

 tail in the crustacean, Mysis, or whether it represents a struc- 

 ture originally common to all vertebrates. In birds and mam- 

 mals the pineal process undergoes metamorphoses which give 

 rise to an organ of a glandular, follicular structure. In birds it 

 never attains such length as in selachians and reptiles and it 

 sends out cellular outgrowths which increase by budding and 

 finally breaking up into numerous small follicles. The opinion 

 has been expressed by many (Henle) that because the follicles 

 are filled with spherical cells resembling lymph corpuscles, the 

 pineal body is a lymph-organ. This has been refuted, for gen- 

 etically the follicles are exclusively epithelial structures. In the 

 adult, within the individual follicles are formed concretions, 

 brain sand (acervulus cerebri). 



Eycleshymer (18-92) wrote as follows of the paraphysis 

 and epiphysis in Amblystoma : In embryos of 5 mm. the 

 epiphysis appears as a cresentic evagination in the roof of the 

 thalamencephalon. The lateral walls are formed of several lay- 

 ers of cells, while the dorsal, which comes directly into contact 

 with the superficial layer of the epiblast, has but a single layer. 

 The nuclei undergo a marked migration toward the periphery. 

 In this respect the appearance is strikingly similar to the condi- 

 tions found in the optic vesicles which at this time are strongly 

 evaginated. The presence of pigment at the inner ends of the 

 cells is also a significant fact. From this time until the forma- 

 tion of the lens in the lateral eyes the epiphysis increases in 

 size, its cavity becomes elliptical and is in wide communication 

 with the thalamocoele. At the time of the invagination of the 

 lens there appears in the posterior portion of the roof of the 

 prosencephalon a second median outgrowth which is directly 

 homologous with the paraphyses described in Reptilia by Selen- 



