ArtificiaUy Produced Cyclopean Fish 33 1 



degrees of cyclopia. The eggs of this salamander when constricted 

 about the periphery of the first plane of cleavage with a fiber- 

 like ligature gave monsters with two equal heads. When the lig- 

 ature was oblique with reference to this plane one of the heads was 

 cyclopean to a greater or less degree. Spemann thought the 

 defective head due to the loss of the anlagen of certain parts, con- 

 sequently these parts never began development and organs sit- 

 uated lateral to them developed in contact from the start. In other 

 words parts between the eye anlagen fail to form and thus the 

 anlagen come in contact and so develop from the beginning. This 

 explanation is of course entirely speculative, but it is supported in 

 a manner by experiments which according to Mall ('08) Lewis 

 has performed on the fish embryo. Mall states that Lewis found 

 by pricking the extreme anterior end of the embryonic shield in 

 Fundulus eggs that many of the eggs develop into cyclops embryos. 

 It was found in some that the prick had destroyed the "nose" 

 only. "This experiment shows conclusively that it is the absence 

 of tissues between the eye arlagen that allows them to come 

 together and unite." 



The above explanation no doubt holds for some cases of cyclo- 

 pia produced by cutting or pricking; there it is evident that tissue 

 is destroyed and the destruction of median tissue may cause the 

 regions containing the eye anlagen to unite. It is difficult to apply 

 this explanation to all cases. In the "Magnesium embryos," 

 why should tissue between the eyes fail to form and not other 

 tissues; why are the nasal pits united in some cyclops and separate 

 in others ? A close microscopic examination of the brain floors 

 in cyclopean and two-eyed embryos shows no absence of recog- 

 nizable parts in the former. The monstra monophthalmica asym- 

 metrica are also to be explained; here one eye in some cases fails to 

 come off from the brain. Is this due to the absence of its early 

 anlage ? The very small cyclopean eye sometimes buried deeply in 

 the head, and the eye shown in Fig. 38 which is partly inclosed 

 within the brain, as well as the entire absence of an eye, suggest 

 another explanation that may apply to all cases in the magnesium 

 solutions. 



The small eyes close together, cyclopia in various degrees, the 



