288 SCIENCE PROGRESS 



So far it had been generally supposed that the " eye " was an 

 unpaired median structure formed by the constricting off of 

 the distal extremity of the pineal outgrowth or epiphysis, and, 

 according to Baldwin Spencer, the constricted portion of the 

 latter actually persists in some cases (e.g. Sphenodon) as the 

 nerve of the pineal eye. Strahl and Martin in 1888, however, 

 showed that the nerve really originates quite independently, a 

 conclusion shortly afterwards confirmed by the researches of 

 Beranek upon the development of Anguis ; while Gaskell, in 

 1890, appears to have been the first to raise his voice against 

 what may be termed the cyclopean dogma of the " median eye." 

 Gaskell argued strongly in favour of the paired character of 

 the pineal sense-organs in the larval lamprey ; but, unfor- 

 tunately, the startling character of his theory as to the origin of 

 vertebrates, which he endeavoured to support by this argument, 

 seems to have prevented his observations from receiving due 

 attention. Gaskell's views as to the arthropod-like structure of 

 the pineal eye have, indeed, not been confirmed by subsequent 

 investigators ; but his opinion as to its paired character has 

 been strongly supported from several directions. The work 

 of Charles Hill (1891 and 1894) on the development of paired 

 epiphysial outgrowths in teleost and ganoid fishes, that of 

 Locy (1893-4) on the development of accessory optic vesicles 

 in elasmobranchs, that of Cameron (1903 and 1904) on the paired 

 origin of the epiphysis in Amphibia and birds, that of Dendy 

 (1899 and 1907) on the development of the pineal organs in 

 Sphenodon and on the corresponding organs in Geotria, all tend 

 to show that the pineal eye, though now apparently median, 

 is in reality one member of an original pair. This question 

 cannot, however, as yet be regarded as finally settled ; for 

 although most writers now admit the double character of the 

 organs in question, some maintain that they do not form a pair, 

 but were primitively developed one behind the other, as they 

 actually appear in many cases at the present day, and have not 

 acquired their antero-posterior relations by secondary displace- 

 ment, as we believe to be the case. 



We cannot conclude this brief historical introduction without 

 referring to the excellent researches of Studnicka, who since 

 1893 has taken the lead in the investigation of the minute 

 histology of the pineal or parietal organs, and who has also 

 given us an admirable general account of these organs in 



