224 



Mary Isahelle Steele 



perhaps should not be counted either way. There were then 

 seventeen negative cases against a single positive case. 



The eye stalks of Crangon are very short and the sections of the 

 optic ganglion are crowded very close together, and extend well 

 into the base of the stalk. Hence it not infrequently happened 

 that a part of the ganglion remained in the stump. A number of 

 these stumps have been sectioned and none of them show any 

 regenerated tissue except the hypodermis and cuticle. Spots of 

 pigment are often seen at the end of the stump but since the whole 

 stalk of the normal eye is heavily pigmented this does not seem to 

 be significant. Figs. 24, '^'J, 40 and 42 show a variety of appear- 

 ances which the stumps presented. The accompanying table 

 shows the number of moults which occurred. 



In some cases the eye stump is extremely short while in others 

 it is longer so that a part of the ganglion remains. All of the 

 specimens included in the table except No. 17 have been sectioned 

 but none of them show any signs of regeneration. Sections of No. 

 10 show that nearly half of the optic ganglion was left but no 

 regeneration is taking place. A very much folded and wrinkled 

 cuticle with short hairs projecting from it covers the stump. Even 

 No. 8 (Fig. 37), short as it appears, is found to contain the proxi- 

 mal end of the optic ganglion. In this case the stump has merely 

 healed over but no new tissue has developed. In several other 

 instances not shown in figures the eye had been totally removed so 

 that not even a short stump is visible. In most such cases the 

 cuticle is wrinkled over the spot where the eye had been. The 

 wrinkles and folds on some of the stumps figured shows the com- 

 mon tendency. These folds are chiefly due probably to the 

 shrinking of the inner tissues of the stump. 



