240 E. I. WERBER. 



sich heraus," he transplanted (in a number of experiments) a 

 fragment of the iris under the skin of the head. The result was 

 negative, as the piece of iris disintegrated and was resorbed. 



Wachs concluded from this result that the site of this trans- 

 plantation was apparently unfavorable and he, therefore, in the 

 next experiments transplanted a fragment of the iris into the 

 otic labyrinth, after first removing a part of the latter. The 

 following results were obtained: 



In several cases where the fragment was "small," i. e., con- 

 sisted of iris only without retinal cells or with some^very few of 

 the latter, no lens-like structures were formed. In a number of 

 instances, however, where the fragment was "larger," i. e., con- 

 taining more retinal cells, lentoids were formed (apparently from 

 the iris), while in several other cases the transplanted fragment 

 was transformed into a small eye with a lens, which latter Wachs 

 considers as formed from the fragment of iris. However, in a 

 number of instances (pp. 425, 426-428) where the transplanted 

 fragment contained many retinal cells and was in good condition 

 ("trotz guter Erhaltung") no lens-like structures were formed. 



These results are, obviously, inconclusive. They certainly 

 do not permit of Wachs 's conclusion that the lentoids and lenses 

 of the "positive" cases owe their origin to a stimulus from a 

 secretion of the retinal cells (carried with the transplanted frag- 

 ment of iris). For, why could not such effect of the retinal 

 "secretion" be observed in the "negative" cases in spite of con- 

 siderable retina? From these results I can read no definite, 

 unmistakable, answer to the question which they were to answer. 



For the following reasons, however, I should regard the query 

 as a very pertinent one. 



We know that the retina (Spemann, Lewis, Le Cron, Bell, 

 Ekman, Werber and others) can furnish the stimulus for the 

 formation of a lens from an epithelial derivative of the ectoderm 

 (even epithelium of the mouth Mencl, '08, and Werber, 'i6r) 

 by contact with it. Besides being capable of furnishing the 

 stimulus for this "lentogenic reaction" the retina (an ectodermal 

 derivative) is according to Fischel's ('oo, '02) and my (Werber, 

 'i6c) observations capable also of responding to such a stimulus 

 the lentoids of the retina. Whence does this stimulus issue in 



