290 Adjustment to Conditions of Aquatic Life 



FIG. 177. Glochidia and their development, 

 into larval mussels, a, b, c, d, stages in the 

 encystment of glochidia of the mussel, Ano- 

 donta, on the fin of a carp; e and /, young 

 mussels (Lampsilis) a week after liberation from 

 the fish; g, glochidium of the mussel, Lampsilis, 

 before attachment. (After Leiavre and Curtis). 



h, glochidium of the wash-board mussel, Quadrula 

 heros, greatly enlarged and stained to show the 

 larval thread (/ and sensory hair cells (5 h c) 

 The clear band is the single adductor muscle. 



*, a gill filament of a channel cat-fish bearing 

 an encysted glochidium of the warty-back mussel: 

 the eyst is set off by incisions of the filament. 

 The darker areas on the edges of the valves indi- 

 cate new growth of mussel shell. (After Howard.) 



j, Encysted young of Plagiola donaciformis, showing 



great growth of adult shell, beyond the margin 



of glochidial shell much greater growth than 



occurs in most species during encystment. (After 



Surber.) 



of the glochidia in a 

 way that parallels the 

 response of a plant to 

 the stimulus of a gall 

 insect. As a plant 

 develops a gall by new 

 growth of tissue about 

 the attacking insect, 

 and shuts it in and 

 both shelters and feeds 

 it, so the fish develops 

 a cyst about the glo- 

 chidium and protects 

 and feeds it. The tis- 

 sues injured by the 

 valves of the glochi- 

 dium produce new 

 cells by proliferation. 

 They rise up about the 

 larva and shut it in 

 (fig. 177). They sup- 

 ply food to it until the 

 metamorphosis is com- 

 plete, and then, when 

 it is a complete mussel 

 in form, equipped with 

 a foot for burrowing 

 and with a good sys- 

 tem of nutritive or- 

 gans, they break away 

 from it and allow it 

 to fall to the bottom. 

 Since this period lasts 

 for some weeks, or 

 even in a few cases, 

 months, the fishes by 



