106 GEORGE LEFEYRE AND WINTERTON C. CURTIS 
(fig. 9) that the fin tissue appears unable to overgrow the mass 
of glochidia and they then remain attached without overgrowth 
for a week or more. Fig. 10 shows how, in a part of the fin 
having no overcrowding, normal embedding occurred; while in 
the more crowded areas the glochidia were still uncovered e\en 
seven days after infection. In the region of tne middle upper 
margin of this figure, it would seem that the overgrowth might 
well have taken place; for many cases, like fig. 11, have been 
observed m wh^ch glochidia as closely set were properly embedded. 
The failure of overgrowth in this region is probably due to the 
presence immediately after infection of a greater n amber of 
glochidia, many of which have since been detached. In all cases 
of this kind, a smaller number will finally become embedded than 
in an infection where the fin has received more nearly the opti- 
mum load (figs. 7, 8 and 11), for the great majority drop off when 
the fin becomes so mutilated that bacterial or fungus infection 
sets in. These over-infections sometimes cause so much hyper- 
trophy that the fins become lumpy and the rays so much drawn 
together that it is impossible for the fin to spread out normally. 
Often, the fins are raw and bleeding for some days and show red 
areas within where the blood vessels have become abnormal. The 
fish are likely to die from this, or from the similar injury to their 
gills, and these over-infections are unsatisfactory, if one wishes to 
bring through their parasitism the maximum number of glochidia 
per fish. 
The steps in the implantation of the glochidium by an over- 
growth of the fish's tissue may be seen in figs. 7-11 and 20- 
23. Figs. 7 and 20 show the glochidium three and one-half hours 
after the fish was removed from the infection. Most of the glo- 
chidia have bitten deep enough in from the margin to have a good 
hold for their hooks. The beginning of the hypertrophy appears 
as a faint mass of tissue, seen with its nuclei in the detailed 
fig. 20. At the end of twelve hours, the overgrowth is well ad- 
vanced and sometimes, as fig. 21, shows different stages even in 
neighboring glochidia. The ragged edge of the host's tissue rises 
up crater-like about the glochidimn, meeting above in a delicate 
mass, the nuclei of which are shown. Fig. 8 shows that, in twenty- 
