582 GEORGE H. BISHOP 



Stage D. In figure D is pictured a stage which differs from the 

 two former stages figured not only in the mechanical arrangement 

 of the cytological elements, but evidently in the nature and con- 

 dition of the substances present. Both nucleus and cytoplasm 

 show marked changes from the previous stage. In the cj^toplasm 

 the peripheral vacuoles have decreased in size and number, while 

 a layer of them has appeared centrally along the sides of the 

 oval nucleus. Early in this stage the nuclear membrane has 

 either disintegrated or lost its precise staining capacity, and the 

 nuclear granules have become more scattered than previously 

 throughout an area more elongated than the oval of the former 

 nucleus. Finally, in the cytoplasm, and especially out from the 



be gathered into one laj'er at the cell's periphery whose thickness would be about 

 one-fifth the radius of the cell. But gathered into one vacuole (as in fig. 1), the 

 globule's diameter would be nearly four-fifths that of the cell, and must push the 

 nucleus to one side. With the fat in smaller vacuoles relative to the size of the 

 cell, the center of the cell may be free from fat (fig. C.) 



The vacuoles of the larger cells are not much larger than the prominent ones of 

 the earlier stage. The reason for the limit to the size of the vacuoles, which seems 

 to be the factor causing the difference of appearance between them, may be 

 deduced tentatively from a consideration of the relation of the volume of a sphere 

 to its absorptive surface. Considering the fat-cell as a chemical plant for the 

 metabolism of fat as well as a storehouse for the product, the chemical activity 

 must take place somewhere between the cell wall and the vacuole where it is 

 deposited. The fat is presumably condensed into vaculoes from the emulsoid 

 form, from the peripheral cytoplasm where it is elaborated. In a small cell the 

 distance is small through which material must be transported from any part of the 

 surface to the one large vacuole, but with growth of the cell the distance increases, 

 and, moreover, the volume of the cell and presumably, the rate of fat metabolism, 

 increase even faster — as the cube of the linear distance. A number of relatively 

 small vacuoles dispersed through the cell's substance, and especiallj^ near its 

 surface, where the material for fat production must be received from the blood, 

 will furnish more surface and distribute this surface more effectively for the 

 accretion of fat than one large one, and as the rate of fat production is increased 

 small vacuoles will be condensed before the material can be transferred to the 

 original large one. Moreover, the ratio of surface to volume would be greater 

 in many small vacuoles then in one large one, and the small vacuoles would conse- 

 quently 'grow' faster, which would make for uniformity of size. The anatomical 

 developments satisfy this hypothesis, without demonstrating its finality. As 

 the cell diameter increases, the fat tends to be deposited in smaller and more 

 peripheral vaculoes, and especially in the queen larva, where the development is 

 most rapid and the cells are largest, the fat-vacuoles are both relatively and 

 actually smaller than in the worker. Differences in consistence of the cytoplasm 

 may also effect the size of vacuoles. 



