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 Le^vre and Curtis). 



h, glochidium of the wash-board mussel, Quadrula 

 heros, greatly enlarged and stained to show the 

 larval thread (I t) and sensory hair cells (s 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 cyst 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. 

 vSince this period lasts 

 for some weeks, or 

 even in a few cases, 

 months, the fishes by 



