Regeneration in Compound Eyes of Crustacea 183 



tissues disintegrate much more slowly than in Palaemonetes, her- 

 mit crabs or crayfish. 



C METHOD OF CELL DIVISION 



In the earlier preliminary stages of the regenerative processes 

 it is impossible to distinguish cell outlines. We should there- 

 fore speak of nuclear divisions, perhaps, instead of cell divisions. 

 In later stages the cytoplasm becomes differentiated about the 

 individual nuclei. In all cases of the regeneration of the eye the 

 nuclei are increased by amitotic division. Before a definite 

 hypodermis is established the nuclei can be seen in various stages 

 of constriction, separating off new nuclei for the development of 

 the future underlying structures. There seems to be no perfectly 

 definite manner in which the constriction and separation of a 

 nucleus into two parts takes place. One or two characteristic 

 forms, however, appear so frequently as to be readily distinguished. 

 The two most usual types are seen in the three nuclei occupying 

 the extreme right of Fig. 53. When a nucleus divides in a plane 

 parallel to its long axis it usually assumes the form of the outer one 

 of the three referred to. The formation of the notch on one side 

 gives the nucleus a peculiar heart-shaped appearance which seems 

 characteristic and is easily recognized. Figs. 49 and 53 show 

 nuclei of this same type further advanced in division. The other 

 type referred to is represented by the other two nuclei of the three 

 at the extreme right of Fig. 53. Apparently these two nuclei were 

 recently formed by the longitudinal division of one of the heart- 

 shaped nuclei, like the one lying beside them. Each of these two 

 is now dividing unequally by a transverse constriction. 



A dividing nucleolus can sometimes be seen but more frequently 

 a definite nucleolus cannot be distinguished. When nucleoli are 

 seen in dividing nuclei they usually appear with a darkly staining 

 strand of material connecting them. In sections of young Cam- 

 barus gracilis eye, nine and sixteen days after the operation, two 

 nucleoli can be recognized in many of the nuclei. In those nuclei 

 that are dividing one nucleolus lies in each part. In all except in 

 the later stages of regeneration of the eye nuclei dividing amitot- 



