771 



may represent the fused second pair of optic cups that Lacy has 

 shown to exist in Squalus? The fact that the two outgrowths from 

 it are situated one behind the other might be accounted for by 

 supposing that the developmental tendency which brought about a 

 fusion of the two into a single median one in Squalus, may in 

 Lacerta have operated so far as to cause an antero-posterior dis- 

 placement of them. 



On the whole it seems to me that, in the present state of 

 knowledge of the subject, there is rather more probability that the 

 parapineal organ will ultimately find its explanation in the paired 

 condition of the primitive pineal eye, than there is in the alter- 

 native explanation; viz., that there existed primitively more than one 

 unpaired pineal eye. 



But our knowledge of the whole subject is so fragmentary that 

 generalizations based upon it and made in the light of Lact's 

 interesting observation, must be very unsatisfactory. One of this 

 author's conclusions is that the epiphysis is homologous with the 

 lateral eyes. But in connection with this conclusion he remarks 

 parenthetically that its "differences in structure need to be explained". 

 This remark is timely and may well be extended to numerous other 

 difficulties involved in the subject. At no time since the epiphysis 

 and pineal eye has been a topic of investigation has it been more 

 interesting or a more inviting one for study than it is just now. 



Berkeley, Cal., May 3, 1894. 



Literature. 

 1883. Ahxbobn, F., Untersuchungen über das Gehirn der Petromyzonten. 

 Zeitschr. f. wiss. Zool., Bd. XXXIX. 



1892. Beraneck, Ed., Sur le nerf parietal et la morphologie du troisieme 

 ceil des verte'breV Anat. Anz., Jahrg. VII, p. 674 — 689. 



1893. — , L' individuality de l'ceil parietal. Anat. Anz., Jahrg. VIII, 

 p. 669—677. 



1892. Eicleshymeb, A. C, Paraphysis and Epiphysis in Amblystoma. 

 Anat. Anz., Jahrg. VII. 



1894. Francotte, P., Note sur l'ceil parie'tal, 1' e'piphyse, la paraphyse, 

 et les plexus choroides du troisieme ventricule. Bull, de 1' Acade'mie 

 royale Belgique, Sene 3e, T. XXVII, No. 1, p. 84—112. 



1891. Hill, Ch., Development of the Epiphysis in Coregonus albus. 

 Journal of Morphology, Vol. V, p. 503 — 510. 



1893. Klinckowsteöm, A. be, Le premier developpement de l'ceil pine*al, 

 1' e'piphyse et le nerf parietal chez Iguana tuberculata. Anat. Anz., 

 Jahrg. VIII, p. 289—299. 



1880. Leydig, F. von, Das Parietalorgan. Biolog. Centralbl., Bd. X, 

 p. 278—285. 



