g6 Journal of Comparative Neurology 



Ahlborn independently recognized the similarity which the struc- 

 ture of the "frontal organ" of Leydig presented to the struc- 

 ture of the lateral eyes and pronounced it to be an unpaired, 

 degenerate organ of vision. Since that time the literature of 

 this subject has grown to enormous proportions and at the pres- 

 ent time there seems to be no cessation on the part of scientists, 

 in their endeavors to discover the origin and development of 

 this remarkable structure. The majority of investigators, in- 

 cluding Spencer, de Graff, Strahl and Martin, Francotte and 

 many others, unite in considering the pineal organ as the differ- 

 entiated distal end of the epiphysis ; while Beraneck, who first 

 agreed with the above authors, now considers it an organ devel- 

 oped with, but independent of, the epiphysis, basing his claims 

 upon the study of the embryo of Angiris fragilis. Francotte in 

 his study of the embryo of the same animal interprets the appear- 

 ances to show that the parietal eye is derived from the epiphy- 

 sis. This position is vigorously maintained by de Klinckows- 

 trom (5 i) who attributes Beraneck's failure to find the evidence 

 of separation of the parietal eye to the lack of material at the 

 correct stage of development. His work corroborates Fran- 

 cotte on Angiris fragilis and he figures like relations for Iguana 

 tubciculata. Beraneck figures for the first time a nerve supply- 

 ing this eye and considers it to spring from a cluster of cells 

 cephalad of the origin of the epiphysis. Francotte was not 

 able to trace the proximal connection of the nerve. De Klin- 

 ckowstrom agrees with Beraneck in regard to the derivation of 

 the nerve both in Angiris and in Iguana. Strahl and Martin in 

 Angiris and Herrick (44) in Phrynosoma think the nerve springs 

 from the supracommissure. Leydig believes the parietal organ 

 develops independently of the epiphysis, denies its homology 

 with a sensory organ aud consider the so-called nerve to be 

 only a bit of connective or lymphatic tissue. But Leydig 

 stands practically alone in his views. The homology of this or- 

 gan is now generally accepted as being that of an organ of 

 vision. But its origin, and the origin and relation of the nerve, 

 are still open questions. Beraneck (10) in a reply to de Klin- 

 ckowstrom makes the point, and we think justly, that in the 



