360 Transactions of the Society. 



in the substance of the membrane (in this case), and that these 

 ancestral cells are not special in their nature, as held by Kanvier, 

 but are purely and simply wanderers. 



The relationship between the fat-cells and wandering cells may 

 be even more clearly traced in Fig. 2, from the mesentery of a rat, 

 where, lying between, or rather opposite the space between, two 

 groups of fat-cells, we see a portion of one of those shoals of wander- 

 ing cells, which may always be found on the free surface of such 

 membranes, lying sometimes like the lines of drift rubbish from a 

 receding tide, and at other times in clusters or buds attached by a 

 pedicle, if sufficient care has been taken not to rub or ruffle the 

 surface of the membrane or rudely to wash them away. 



The fact that these cells are to be found scattered over the free 

 surface of such membranes, and unconnected with other structures, 

 is clear proof of their being wandering cells; and when we can 

 trace identity between them and similar cells becoming, or about to 

 become, fat-cells lying between the endothehum-covered surfaces, 

 the direct relationship between the two becomes evident. 



In Fig. 2, with three or four exceptions, all the wandering cells 

 depicted there lie on the upper free surface of the membrane ; on the 

 opposite free surface of the membrane there were quite as many, but 

 to prevent confusion we have not drawn them. For the same 

 reason, we have only drawn the endothelium outlines on the upper 

 surface, except at cell a, where we have inserted in dotted lines 

 the outline markings of the endothehum on the lower surface of 

 the membrane, in order to show cleai'ly that cell a lies between the 

 surfaces in the substance of the membrane, and that it is identical 

 with cells c and d lying on the free surface, and forms a link 

 between these and cell h lying, like itself, between the endothelium- 

 covered surfaces, and which, as is shown by the two fat-globules within 

 it, is rapidly becoming a fat-cell belonging to the group of which 

 cell / is a fully developed fat-cell. 



It has been urged as a reason for holding the progenitor of the 

 fat-cell to be a special form, distinct from the wandering cell, that 

 the latter is globular and the former flat and round ; but a glance at 

 such a group of wandering cells as is shown in Fig. 2 lets us see 

 both forms, with every variety of gradation between them. Young 

 wandering cells like d have so little protoplasm round their nucleus, 

 that they retain the globular form when exposure to cold or to silver 

 solution has forced them to retract their amoeboid processes and die 

 on the spot. 



Full-grown wandering cells, on the other hand, with abundance 

 of protoplasm round their nucleus, like cells c, c, remain spread over 

 a certain extent of surface when subjected to the same conditions 

 as those affecting cells d, d. Every gradation of form may be seen 

 between these two extreme types, and we may also note that, when- 



