246 ALFRED SCHAPER. 



ments is of very great interest, in so far as it gives a new evi- 

 dence of the equipotcntial nature of tlic ectoderm elements during 

 a certain early period of development. However in further dis- 

 cussing his grafting-experiments and some other observations 

 made in connection with them Lewis is also led to a criticism of 

 a theory recently advocated by me, namely tliat the lens lias to be 

 considered as a modified primitive sense organ. As this criticism 

 seems to be based upon a misconception of my article on this sub- 

 ject 1 I feel induced to write the following remarks in explanation. 



Lewis says on page 535 of his paper : Schaper's theory " will 

 not hold in view of the fact that the ectoderm, taken from over 

 the abdomen of R. sylvatica and grafted on over the optic vesicle 

 of R. pahistris (see experiment XII., 51), did not possess at the 

 time of operation the primitive sense organs and yet it gave rise 

 to a lens. Again it seems unlikely that in several instances in 

 which I have been able to bring about lens formation from a 

 strange ectoderm that the optic vesicle should have in each case 

 come in contact with one of these sense organs. And again in 

 such experiments as IV., in which the optic vesicle has never 

 been in contact with the ectoderm which normally gives rise to a 

 lens there is no trace of a rudimentary lens such as Schaper 

 pictures." From this remark it is obvious that Lewis holds, that 

 according to my opinion the lens should arise in the course of 

 ontogetietic development from a preformed primitive sense organ 

 of the skin. 



In refutation of this, the following must be said. In the first 

 place I have to state that nowhere in my above cited paper have 

 I spoken of a preformed primitive sense organ (" Sinnesknospe ") 

 as being the onlogenetic forerunner of a lens. What I have main- 

 tained is, that the structure which arises from the stimulated part 

 of the ectoderm, to form the lens, shows in its development and 

 its primitive histological features a striking resemblance to a 

 primitive sense organ of the skin, and that this resemblance be- 

 comes still more striking when, as in my experiments, by atypical 

 development the lens-anlage is retained within the ectoderm. The 



1 Schaper, A., " Ueber einige Falle atypischer Linsenentwirklung unter abnormen 

 Bedingungen. Ein Beitrag zur Phylogenie der Linse und zur Mechanik ihrer Ent- 

 wicklung," Anatom. Anzeiger, XXIV., 1904. 



