32 UNIVERSITY OF MISSOURI STUDIES [220 



place, and the pigment-cells approach, to a certain extent, the 

 normal arrangement. On the other hand, however, there is no 

 indication at all that the optic ganglion, the crystalline cones and 

 corneal facets are regenerated; and, furthermore, the cuticle 

 over the pigmented region is as thick as it is over the stalk. It 

 is true that, when only a part of the cornea is removed, as in the 

 case cited on pp. 29-30, the remaining portion may continue to be 

 entirely functional, but here the connection between the ganglion 

 and the ommatidial region has not been completely severed. 



(b) Regeneration After Removal of the Entire Eye. — 

 This portion of the subject includes, perhaps, the most in- 

 teresting phase of the question. There are in these experiments 

 results which are at least definite, even though but little under- 

 stood. However, they are not more inexplicable than other 

 heteromorphic structures. 



Whenever the entire eye, together with the whole or 

 greater part of the eye-stalk, is removed, the eye as an organ of 

 sight is never regenerated. A new structure may, and in many 

 cases, does develop, but instead of an eye it is a different kind of 

 appendage. Usually this structure is jointed, sometimes like the 

 flagellum of an antenna, but in other cases a pair of flagella like 

 those of the antennules are formed ; and again the structure may 

 have no resemblance whatever to a normal appendage but con- 

 sists of a short two or three- jointed structure similar neither 

 to the eye nor to any appendage the crayfish possesses. The last 

 mentioned structure resembles the appendage that Herbst (loc. 

 cit., pp. 545-6) designated as horn-like (horndhnlichen) . In dis- 

 cussing the results obtained after removal of the entire eye, I 

 shall refer to a series of crayfish which illustrate the different 

 forms that the regenerated structure may assume. 



Type I : A pair of flagella regenerated. The first instance 

 observed of the development of these peculiar heteromorphic 



