2.5Ü GroH'th of Cell in Daplinla Magna 



Tlic diameters of thc diainond-shaped are;is of the carapace are therefore 

 rcgardcd as giving us a concoption of the sizes of the cpidermal cells of that 

 region. Oiily regulär diamond-shaped areas were measured and in this way most 

 of thc ineasurcs would strictly correspond to ccUs. The fact that in some cases 

 there may have bcen unavoidably inchided areas correspondiiig to two cells will 

 not affect the comparative results because such would occur as often in the young 

 as in th(> fully-grown animals. 



Fio. 1. 

 The dimensions takcn were : 



(1) The length of the body, measured fmia the anterior convexity of the 

 head in front of the Compound eye to the base of the dorsal spine. 



(2) Thc diameters of 10 diamond-shapcd areas over thc middlc lobe of the 

 maxillary gland, and measured in the vertical direction. (See Fig. 1, ABD, the 

 arrovv indicates the direction of measurement.) 



The daphnia were taken from a large tank at University College, London, and 

 201 animals of varying sizes were measured. 



Thc measiircmcnts were made with an oeular micromcter, and ander such 

 magnification that a division of thc micrometer scale in mcasuring the body-length 

 was =00320 mm., and the cell-lcngth =000385 mm. 



The accompanying table gives the correiation surface for the length of daphnia 

 and diamctcr of carapace ccll.s. For thc working scalc thc unit of length for thc 

 body was five divisions of the oeular micromcter =0100 mm., and for the cell 

 dimension =0'01925 mm. 



The linc of means for the arrays is represented in the annexed diagram. 

 There is clcarly a considcrablc correiation betwecn the size of the body and the 

 size of the cells, and this correiation is much grcatcr ;il the younger periods 

 of growth than it is at any later period. 



