Io8 BULLETIN OF THE BUREAU OF FISHERIES. 
The only fish so far taken carrying what is apparently recent infection is one taken October 
21, but only a few, about i per cent, are of this stage, i. e., the glochidium still simple. 
The next stage is indicated in specimens secured October 15, where the growth is quite 
decided, the infant mussel having assumed a nearly circular form when viewed from the 
side; this phase is clearly shown in figures 2 (side ^dew) and 3 (postero or antero ventral 
view). In figure 2 the larval mussel is on the extreme tip of the gill filament, while 
figure 3 is encysted about 3 mm. back from the tip and on the flat side of the fila- 
ment. Another fish, taken October 30, holds larval mussels in a more uniform state of 
development, of a stage clearly shown by figure 4; by reference to this figure it will be 
found that the young mussel has apparently grown more rapidly in length than in 
height, and that in the region of the umbones, both anteriorly and posteriorly, it has not 
grown at all, except in thickness, giving it a curious depressed effect there. Figure 4 
exhibits the sharpness of the ventral points of the glochidial shell on the upper side, 
caused by the growth of the shell of the young mussel expanding the glochidial shell; 
in figure 5 a dorsal view is given of another specimen of the same relative development 
to show increase in thickness. 
The greatest development seems to be reached during October, when they have 
assumed the shape and size indicated in figures 6 and 7, where it has increased three to 
four times in length over glochidium and the inflation (thickness) is so marked as to 
suggest anything but the parent shell, when viewed dorsally (fig. 7). This stage has 
been shown before (Coker and Surber, Biological Bulletin, vol. 20, p. 179-182, fig. 5, 
6, and 7). It is believed that at this stage the parasitism is completed, or nearly so, 
and this belief is strengthened by the fact that on November 2 a fish was taken holding 
comparatively few (120) mussels and a number of ruptured cysts which had probably 
held others a very short time previously, though it is of course possible that the ruptures 
may have been caused by other parasites, but this is not deemed probable. We might 
infer from this that the fish became infected either the preceding spring (1912) or during 
September of the preceding year (1911), the latter seeming the more probable. Leevis- 
sima with ripe glochidia has been taken in the vicinity of Fairport during April, June, 
and September. 
So far, this mussel has been found on but one other species of fish, the crappie, in 
which the same development is indicated as occurs in the sheepshead. 
Table I. — Number of Larval L. l^Evisstma Carried by the Host. 
Species of fish. 
Date 
secured. 
Number 
of glo- 
chidia. 
Ix)cality. 
Aplodinotus grunniens 
June 16,1910 
670 
Fairport, Iowa. 
Oct. x8, 1910 
375 
Do. 
Oct. 15,1912 
32s 
Do. 
Oct. 17,1912 
112 
Do. 
Oct. IS, 1912 
850 
Do. 
Oct. 30,1912 
200 
Do. 
Oct. 21,1912 
240 
Do. 
Nov. 2, 1Q12 
120 
Do. 
Nov. 9, 1912 
540 
Do. 
Nov. 17,1912 
112 
Do. 
Nov. 21, 1912 
210 
Do. 
