On the Rhizocephalan Genus Thompsonia, etc. 



11 



secondary root to each external sac and generally a number of others 

 which ended in club-shaped swellings. The significance of these last 

 will be explained later. 



It thus became evident that the root systems of adjacent sacs at least 

 were continuous, and since all the sacs upon one host are in the same 

 stage of development, it was hardly to be doubted that the one system is 

 common to all. Dissections of the trunks of infected Alpheids were 

 made and carefully examined for roots. A perfect network of slender 

 grey roots was seen to exist in the ventral body wall and to be concen- 

 trated particularly in the neighbourhood of the nerve cord. 



The course of the root system in the body of the host particularly 

 was best demonstrated, however, in preserved material. The infected 

 animals were preserved for further study by fixing either with corrosive 

 sublimate solution or Flemming's fluid. In those treated in the former 



FIG. 2. Abdominal appendage of Synalpheus brucei 

 infected by Thompsonia; to show the branch- 

 ing root system connecting a number of very 

 young external sacs. The specimen was fixed 

 in corrosive sublimate and stained with borax- 

 carmine. The roots have therefore taken up very 

 little stain compared with the tissues of the host 

 and are shown unshaded, v.m., visceral mass; 

 m., mantle; p., peduncle; cl., internal bud of 

 root system, which after further development 

 will become an external sac. X35. 



:7 



manner the results are not very satisfactory. It is only possible to 

 trace the roots because they take-up stains so much more slowly than 

 the surrounding tissue. In text-figure 2 an abdominal appendage is 

 represented which bears a number of young external sacs. This was 

 stained in a very dilute solution of borax-carmine for several days. 

 The roots connecting the sacs are shown as colourless channels in the 

 well-stained epithelial tissue of the appendage. 



But much clearer preparations were obtained from the individuals 

 fixed in Flemming's fluid. In appendages from these mounted in 

 Canada balsam without any further staining, the course of the roots 

 is shown with the greatest clearness by the yolk granules, which are 

 blackened by the osmic acid in the fixing fluid. The majority of the 

 drawings which I reproduce here to illustrate the root system have been 

 made from preparations of this kind. 



