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. Theroots 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. 
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. 
