l8o Mary Isabelle Steele 



uninjured ommatidia have regained their original shape and 

 position. This temporary contortion of the ommatidia seems to 

 be due to the immediate effects of the operation, reduction of 

 pressure, destruction of normal tension relations, etc. That in 

 the later stages they appear normal again indicates that they have 

 adjusted themselves to the new conditions imposed upon them by 

 the operation. 



Besides those ommatidia that are actually injured by the 

 operation a large portion of those remaining frequently degenerate. 

 The destruction of the tissues of the eye is, consequently, much 

 more extensive than the original injury. This fact is strikingly 

 illustrated by eyes in which the original injury consisted in thrust- 

 ing a needle into the ommatidial portion. In several such in- 

 stances the entire, or almost the entire, eye has degenerated. 

 Instances of this kind have been observed in the eyes of sev- 

 eral Palaemonetes and also in the eyes of young Cambarus gracilis. 

 Similar phenomena have been observed in eyes of fresh water 

 Gammarus. To be sure the eyes of Gammarus are quite small 

 which may account in a measure for the fact that in six or eight 

 eyes examined in serial sections only one showed any of the old 

 ommatidia intact. In Cambarus gracilis there were two instances 

 out of six in which none of the ommatidial portion remained. In 

 one of the cases the entire eye had degenerated; not even the vestige 

 of the stalk remained. All of this degeneration took place in 

 about thirty days and without a moult. In the other case all of 

 the ommatidial portion and more than half of the optic ganglion 

 had degenerated during the same period. In other eyes of the 

 same series very little degeneration followed the operation. In 

 these extreme cases it seems probable that some infection played 

 a part. 



In the degeneration and removal of the injured tissues the 

 retinulae degenerate most rapidly. In many cases they break 

 down within the first few hours after the operation. Their long 

 pigmented processes become separated from the cell body and 

 collapse into shapeless masses of pigment, which become scattered 

 through the other tissues. The greater part of this pigment 

 finally gathers in clumps near the level of the basement mem- 



