Glochidia 291 



wandering from place to place aid the distribution of 

 the mussels, but they do much more than this. 



It is to be noted, furthermore, that this relation is a 

 close one between particular species, just as it is be- 

 tween plants and gall insects. Each attacking species 

 has its own particular host. Recent careful studies 

 made by Dr. A. D. Howard and others at the Fairport 

 Biological Laboratory have shown such relations as 

 the following: 



species of Mussels Host Species 



1. Yellow Sand Shell (Lampsilis anodontoides) on the gars 



2. Lake Mucket (Lampsilis luteolus) on the basses and perches 



3. Butterfly Shell (Plagiola securis) on the sheepshead 



4. Warty Back (Quadrula pustulosa) on the channel catfish 



5. Nigger-head (Quadrula ebeneus) on the blue herring 



6. Missouri Nigger-head (Obovaria ellipsis) on the sturgeons 



7. Salamander mussel (Hemilastena ambigua) on Necturus 



Some of these mussels infect one species of fish ; some, 

 the fishes of one family or genus ; a few have a still wider 

 range of host species, these last being usually the 

 species having the larger and stronger glochidia with the 

 best development of clasping hooks on the valve tips. 

 A very special case is that of Hemilastena, a mussel 

 that lives under flat stones and projecting rock ledges 

 in the stream bed. Living in the haunts of the mud- 

 puppy, Necturus, and out of the way of the fishes, it 

 infects the gills of this salamander with its glochidia. 



The glochidia will grow only on their proper hosts. 

 They will take hold on almost any fish that touches 

 them in a manner to call forth their snapping reaction, 

 but they will subsequently fall off from all but their 

 proper hosts, without undergoing development. 



Whether it be the mussel that reacts only to a certain 

 kind of fish substance, or the fish that reacts to form a 

 cyst only for a certain glochidial stimulus is not 

 known. The relation appears onesided, and beneficial 

 only to the parasitic mussel; yet moderate infesta- 



