8 UNIVERSITY OF MISSOURI STUDIES [^9^ 



The fourth series of experiments ('99), deals chiefly with 

 results obtained after removal of only a portion of the eye of the 

 stalked-eyed Decapods, Palaemon and Palintirus, and the entire 

 eye of the sessile-eyed Porcellana. The experiments, however, 

 also included the removal of the eyes of the Isopods, Idothea 

 tricuspidata and Sphaeroma serratum, and Paliniirus vulgaris 

 and several species of Palaemon were used in the removal of 

 only a part of the eye. The cuts removing a part of the eye were 

 made at various angles and at different levels, but in all cases the 

 whole or greater part of the eye-stalk was spared. Results of 

 these experiments differed from previous results in that the re- 

 generated structure resembled not an antenna but an eye, not ex- 

 actly normal to be sure, but showing a regeneration of pigment 

 and, in some instances at least, the suggestion of ommatidia. 

 Porcellana, after total excision of the eye, regenerated not an an- 

 tenna-like structure but an eye, and indeed in this case the regen- 

 erated eye seems to approach very closely to the normal one. The 

 Isopods, Sphaeroma serratum and Idothea tricuspidata, after the 

 removal of the entire eye, also regenerated eyes. 



The results obtained from all of his experiments led Herbst 

 to the following conclusions: first, the presence or absence of 

 the optic ganglion determines whether an eye or an antenna-like 

 organ shall be regenerated; second, when the optic ganglion is 

 present an eye is regenerated; third, removal of the optic gan- 

 glion causes an antenna-like organ to be regenerated in place 

 of an eye. In support of the second conclusion is the fact that 

 Porcellana, Idothea and Sphaeroma regenerate eyes, although 

 the entire eye has been removed. In these sessile-eyed forms, 

 however, the optic ganglion is directly connected with the brain 

 and consequently is not injured even when the eye is wholly re- 

 moved. Further evidence in favor of this conclusion Hes in the 

 fact that in stalked-eyed forms the eye is regenerated after re- 



