350 E. I. WERBER 



fully adequate. The problem is, as I hope to make clear in the 

 following, pre-eminently a biochemical one, as Lewis has sug- 

 gested already in 1904. 



During the summers of 1914 and 1915 I performed a large 

 number of experiments on fertilized eggs of Fundulus heterocli- 

 tus by exposing the latter in early cleavage stages to some toxic 

 products of pathologic metabolism in order to test the hypothesis 

 that these products may underlie the 'spontaneous' origin of 

 monsters. Among the many monsters thus produced those with 

 terata of the eyes were found to be of most frequent occurrence. 

 In some of the latter free lenses were found. The location of 

 such 'independent' lenses is strikingly variable. Thus, for in- 

 stance, a Cyclopean embryo was once found,- which had besides 

 the lens of the median eye also a free lens, normal in size and 

 structure, in a lateral position (Werber '15 a, fig. 28, p. 551). In 

 a sjrmmetrically monophthalmic embryos a lens of approximately 

 normal size may sometimes be found on the side lacking the 

 eye, or several small -lenses may be met with on various parts 

 of the head in a lateral or anterior position. In such and in 

 anophthalmic embryos one or more small lenses are sometimes 

 found on the anterior tip of the head, while in one asymmetri- 

 cally monophthalmic embryo three small lenses were found on 

 the maxilla (Werber '16 b, figs. 78 and 79). In many instances 

 small free lenses were also observed posterior to one of the eyes 

 in deformed embryos possessing two eyes in the usual lateral 

 position. 



The perfect analogy between these observations and those of 

 Mend's (I.e.) and Stockard's (I.e.) is evident. For in all these 

 cases lenses have developed, without the contact stimulus from 

 an optic cup, from indifferent ectoderm which would normally 

 not have given rise to such structures. If Mend's and Stock- 

 ard's interpretation according to which these lenses are to be 

 considered as products of self-differentiation were justified it 

 would necessarily apply also to the free lenses which I have 

 recorded. Yet, is the evidence of Mencl and Stockard conclu- 

 sive? Will it stand the test of critical examination? I believe 

 that I shall be able to show in the following that these ques- 

 tions cannot be answered in the affirmative. 



