STUDNICKA'S THEORY 



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Studnicka noticed that if one traces the visual-cell side of the inner 

 layer of the optic cup around the latter and through the optic stalk into 

 the central nervous system, one emerges into the ependymal layer of the 

 brain wall. The ependymal cells lining the cavities of the brain and cord 

 are non-nervous supporting elements which often bear flagella (micro- 

 scopic whiplashes) which circulate the cerebrospinal fluid. Studnicka 

 also laid great stress upon the eye of the young larval lamprey (Fig. 54c) , 

 which is precociously functional while still merely an optic vesicle, as 

 indicating that the vertebrate eye was originally merely a 'directional' 



Fig. 55 — Comparability of young visual cells with ependymal and other flagellated cells: 

 embryological support for Studnicka's theory. From Walls. 



a, fetal human foveal cone, showing filamentous, centrosomic anlage of outer segment rooted 

 in diplosome (after Seefelder). b, immature human sperm cell showing anlage of flag- 

 ellum, consisting of centrosomic filament and diplosome (after Gatenby and Beams), c, 

 immature cone from retina of kitten (after Leboucq). d, ependymal cell from brain of 

 carp (after Franz). 



one before it became capable of forming images. Since the lens is already 

 present in the tiny lamprey, but in the form of a flat cushion incapable 

 of dioptric function, Studnicka argued that it must have existed phylo- 

 genetically — a vestigial remnant of something else, possibly a sense- 

 organ — before the retina was devised at all. He also showed that there 

 are many central-nervous sense-organs in vertebrates, including the 

 median or pineal and parietal eyes (see Chapter 10, section D), whose 

 receptors are certainly modified ependymal cells. He has received strik- 

 ing confirmation in the recent demonstrations of the photosensitivity of 

 the lining of the diencephalon of many forms, which (in birds) has been 



