3o8 THE DEVELOPMENT OF THE NYMPH. 



disintegration of the contained cells. I saw small granule 

 cells attach themselves to a fat cell and crawl over it ; others 

 subsequently made their appearance, so that two hours from 

 the beginning of the observation the whole fat cell was covered 

 by these leucocytes; indeed, in this state it resembled a 

 segmented ovum in the morula stage. The appearance per- 

 sisted for a long time, until at length a nest of granule cells 

 entirely replaced the fat cell, and these finally separated and 

 scattered themselves.' 



I have not repeated this observation of Kowalevski's, and I 

 am unable to understand how he obtained a satisfactory view 

 of the process in ihe entire nymph. But I have taken living 

 fat cells from the pupa, spread them over a thin cover, and 

 fixed them with steam, subsequently staining and mounting 

 them. Such preparations sometimes exhibit leucocytes in the 

 act of entering a fat cell with remarkable clearness. 



The changes which occur in the fat cells after the penetration 

 of their external membranes by leucocytes are exceedingly 

 interesting. At first a group of leucocytes is observed sur- 

 rounding the nucleus ; these multiply with great rapidity, and 

 extend in ever increasing numbers outwards towards the cell- 

 capsule. As the leucocytes increase in number, the fat 

 granules gradually disappear and give place to vast numbers of 

 cells, which differ in no perceptible manner from the blood 

 corpuscles of the larva. The cells nearest the nucleus of the 

 fat cells are far larger than those near the periphery, and the 

 former are usually multinucleate. The latter probably originate 

 by the division of the former. 



During the process the envelope of the fat cell disappears, 

 and eventually the peripheral leucocytes become scattered in 

 the blood. For a long time after this the central larger cells 

 cohere around the nucleus, but ultimately they separate and 

 leave the nucleus, which, after a longer or shorter time, 

 appears to be attacked like the muscle nuclei by phagocytes. 

 Isolated nuclei are frequently seen free in the blood of the 

 nymph, and these are usually full of cells which are set free as 

 leucocytes PI. XVI., Fig. lo). 



