A PRELIMINARY ATTEMPT TO ASCERTAIN THE RELA- 

 TIUNSHIP BETWEEN THE SIZE OF CELL AND THE 

 SIZE OF BODY IN DÄPHNIA MAGNA STRAUS. 



By ERNEST WAREEN, D.Sc, Zoological Laboratory, University College, London. 



In the coiirsc dt' investigating the clevelopmeut of the trematode of the crayfish 

 (Dlstointdii corrigerum) it was observed that the uuclei of the general body cells of 

 the developing aiiimal were very niuch smaller thao those of tlie fully-grown 

 croature. On comparing animals of difforent ages it could be readilj' seen that as 

 the body grew as a whole so the individual cells became gradually larger. 



According to tho iisual view that cells are units of very great individuality, 

 growth of the body would imply ä priori siinply an increase in the numher 

 of these units and not a change in their raean size or general character. 



Although in the case of the trematode there was no doubt about tlie intiniate 

 relationship between the size of the body and the size of the cell during a certain 

 period of growth, yet it was desirable to ascertain whether there was a similar 

 relationship in an actively growiug animal of practically adult structure and not 

 merely in a developing embryo. 



For this pnrpose Daphnia appcared to be a suitable subjeet if some measurable 

 cell character could be found in the fresh aiiimal. 



The surface of the carapace of Daphnia magna is covered with diamoud-shaped 

 areas which correspond with considerable exactitude to the cell-outlines of the 

 unileriyiug epidormal cells. A number of daphnia of various sizes were treatcd 

 with picrocanniue. The free picric acid fixed the tissues to a certain exteut, and 

 the nuclei of the epidermal cells were sometimes, although by no means always, 

 stained a very pale pink. It was then seen that typically one nucleus occurred 

 under each area. Fairly frequeutly, however, but especially under any irregidarly 

 shaped areas two nuclei could be seen. In such cases the polygonal area would 

 correspond to two epidermal cells. It was particularly noticed that the occurrence 

 of two nuclei under an area could be observed as frequently in youug aud small 

 individuals as in older and larger specimens. 



