Independent Development of the Lens. 417 
lens-like structure which is entirely free from any contact with 
an optic vesicle. The inaccuracy of the operation may account 
for these lenses, on the ground that in exceptional cases the outer 
ectoderm of the lens region was too far distant at the early stage 
of development to have been injured. This is probable when it is 
noted that the operation did not enter through the lateral ecto- 
derm, but through the partly open medullary tube from above. 
The present evidence also goes to strengthen King’s position on the 
subject. 
Spemann (05), Lewis (07) and LeCron (’07) have all claimed 
that the lens after its origin, was not self differentiating but 
depended upon a durable contact with the optie cup for its 
future development. Ail of the writer’s experiments and the 
observations of Mencl are clearly contradictory to such a view, 
and Spemann (’07) has more recently found the lens to be self- 
differentiating in Rana esculenta. 
In a former paper the writer (’07) described the development. of 
the lens in the blind Myxinoid, Bdellostoma stouti. At that time 
he presumed that this animal furnished support for the experi- 
mental evidence that the lens was not self-differentiating. In 
Bdellostoma embryos the optic vesicle is well formed at first and 
reaches out from the brain to the ectoderm; at this time the ecto- 
derm forms a localized thickening suggesting a lens-plate. The 
optic vesicle then ceases to maintain its progressive development 
and loses connection with the ectoderm, finally giving rise to 
the poorly formed optic cup of the adult. The early lens thicken- 
ing of the ectoderm degenerates and is entirely absent from older 
embryos. The writer suggested that this degeneration was due 
to the loss of contact with the optic vesicle, since such reasoning 
seemed correct in the light of the experiments up to that time. He 
has entirely changed his view, however, regarding the matter of 
the lens in Bdellostoma and now believes that it represents a 
rudimentary organ which has been lost in the adult and appears 
only for ashort time during embryonic life. As Eigenmann (’01) 
records of Amblyopsis, the lenses of other blind fishes appear at 
certain stages in the developing embryo and then degenerate. A 
‘case not so far advanced in the degeneration of the eye and lens is 
THE AMERICAN JOURNAL OF ANATOMY, VOL, 10, No. 2. 
