REPRODUCTIOX IX THE TXIOXID.E 
107 
four hours, most of the glochidia are more than half covered, 
whether upon the edge or the surface of the fins. At the end of 
thirty-six hours, optimum infections of the carp show all the 
glochidia, vvhichhave obtained a proper attachment, well embedded , 
and after this the only external change is a shght increase in opa- 
city which renders the internal structure of the glochidium less 
distinct. Some of our infections show embedding in as short 
a time as six hours (Symphynota) and Harms ('09) gives ten to 
twelve hours, as the time which he obseried in Anodonta, so the 
time given for the figures is the maximum for hooked glochidia 
which have been well located. Glochidia upon the fin surface 
become em.bedded in a similar manner and are then in a very 
secure position. (Figs. 11 and 14b.) 
Infections with hookless glochidia 
Following these same methods of artificial infection, we have 
made more extensive experiments upon the parasitism of the hook- 
less glochidia, which is the only type found in our commercial 
mussels. Species of the genus Lampsihs (ligamentinus, rectus, 
anodontoides, ventricosus, subrostratus and luteolus) have been 
the most used, but infections hare also been made with several 
species of Quadrula and one of Unio. The list of fish employed 
as hosts is also more extensive and we are, therefore, able to make 
statements which we know to be of wider application than those 
made for the hooked forms. 
When the same fish is used, the results for the several species 
of Lampsilis are very uniform and we can thus discuss the para- 
sitism of this genus as a whole: but we do not find the same mus- 
sel giving uniform results with all species of fish. The glochidia 
of this genus have been used successfully for the infection of olue- 
gill sunfish, yellow-perch, crappie, large-mouthed black bass (Mic- 
opterus salmoides), rock bass, the red-spotted sunfish (Lepomis 
humilis) and the green sunfish (Apomotis cyanellus). As with 
the hooked glochidia, the infections have all been made upon fish 
under six inches in length, upon which these glochidia remain in 
numbers only on the gill-filaments, though during infection many 
