200 HELEN L. M. PIXELL-GOODRICH. 



bee increases in age, vacuoles appear at the periphery of the 

 cytoplasm of the nerve-cells, so that even at the end of 

 the first week of toil most of the cells have somewhat the 

 appearance shown iu PI. 11, fig. 6. During the exertions of 

 foraging for nectar, pollen, etc., the brain-cells age still 

 further ; so that a bee returning to the hive at mid-day 

 laden with pollen showed the condition represented in PI. 11, 

 fig. 7. 



The cell shown in PL 11, fig. 8, came from the sub- 

 <]esophageal ganglion of a bee which was unable to fly, and 

 had lost nearly all the hairs on its thorax. There is thus 

 good reason to think that it was senescent. The final stage 

 of disintegration of the cytoplasm is shown in PI. 11, fig. 9, 

 ■one of the cells from the ganglion drawn in PI. 11, fig. 4. 

 This belonged to a bee which came from a hive on a fine day 

 in March, but was too weak to effect a cleansing flight and 

 •soon became moribund. It will be seen that the nerve-cells 

 are quite worn out, there being in this part of the ganglion 

 •only a framework of connective tissues, with here and there 

 the nucleus of a nerve-cell in a more or less necrotic con- 

 dition, with only a trace of cytoplasm roiind it. 



It will be noticed that the nuclei of bee nerve-cells contain 

 several nucleoli as described by Binet (1) for most insects. 

 DoUey (3), however, figures for the crayfish a single largo 

 nucleolus such as is found in typical vertebrates. I cannot 

 agree with Mann (13), Hodge (9), and some others that there 

 is a marked shrinkage of the nucleus due to fatigue. In well- 

 fixed brains the nuclei appear to retain their normal shape 

 and also their size, as shown by Smallwood and Phillips (1^). 

 In very old bees, however, the chromatin seems generally to 

 leave the nuclear membrane and tends to form a single clump 

 jtist inside. 



A reduction of cytoplasm due to fatigue has been previously 

 described by Dolley (3) in the nerve-cells of the crayfish after 

 artificial stimulation. This he refers to as an CBdematous 

 condition, since the so-called vacuoles left at the periphery of 

 the cell as the protoplasm disintegrates become, of course. 



