REGENERATION IN LUMBRICULUS. 279 



MATERIALS AND METHODS. 



The species used in this work was identified for me by Professor 

 Frank Smith, of the University of Illinois, as of the genus 

 Lumbriculus, and probably the species inconstans Smith. An- 

 sesthetization was avoided as far as possible. When it was 

 necessary, a one eighth of one per cent, solution of chloretone 

 or a four per cent, solution of alcohol, redistilled in glass, gave 

 equally satisfactory results. For histological fixation Zenker's 

 fluid or Bouin's Picroformol were used ; best results were obtained 

 with the latter. It was not necessary to anaesthetize the worms 

 first. An individual to be fixed was placed on a glass plate and 

 straightened against a glass slide. Another slide was then 

 pushed up until it came in contact with the worm, care being 

 taken not to crush it between the slides. In this process only 

 a very small amount of water was used. The fixing fluid was 

 then slowly added and its surface tension, as it was drawn 

 underneath the two slides, held the worm firmly in place during 

 the preliminary fixation. This method is a modification of one 

 described by Welch ('13). As a stain Heidenhain's iron alum- 

 hematoxylin method was used for the most part, though prepara- 

 tions were also made with Delafield's hematoxylin and eosin, 

 used both as a direct and as a regressive stain. On carefully 

 controlled regressive staining the chromatin granules were stained 

 with the hematoxylin while the nucleoli took the eosin, indicating 

 that they were true nucleoli or plasmosomes. 



NUCLEI AND NUCLEOLI IN THE CELLS OF UNINJURED 



INDIVIDUALS. 



As this paper is to deal at some length with the cytological 

 changes, particularly nuclear and nucleolar, which occur during 

 regeneration, it is perhaps advisable first of all to discuss more 

 or less completely the conditions which exist in uninjured indi- 

 viduals. Under this heading the usual appearance of cells in the 

 hypodermis, setigerous glands and intestine, including those 

 differences which may exist at the growing region of the tail, will 

 be described. 



