110 ELEMENTARY BIOLOGY. [XI; 



hair-like filaments. What appears to be the oral aperture 

 is wide, and its margins are richly ciliated. There is a single 

 adductor muscle and a rudimentary foot, from which one 

 or two long structureless filaments, representing the hyssus 

 of the sea-mussel, proceed. These byssal filaments become 

 entangled with one another and tend to keep the 'Glochidia' 

 in their places. 



After a time the larval Anod'ontoe leave the body of the 

 parent, and attach themselves to floating bodies — very com-, 

 monly to the tails of fishes — by digging the incurved points 

 of their valves into the integument in the latter , case, and 

 holding on by them as if they were pincers. In this situa- 

 tion they undergo a metamorphosis; the gills are developed, 

 the- foot grows, the auditory vesicles become conspicuous 

 in it, and the young Anodon at length drops off and falls 

 into its ordinary habitation in the mud. 



LABORATORY WORK. 



1. In the natural state of the animal only the shell or 

 exoskeletofi is visible, or this may be slightly open, 

 and then the edge of the membrane lining it (the 

 mantle) may be visible. Raise one valve of the shell, 

 by separating the mantle from it with the handle of a 

 scalpel, and then cutting through two strong bodies {the 

 adductor muscles), one at each end of the animal, 

 which run from oae valve of the shell to the other 

 and prevent their separation. The two valves will 

 now be united only by their ligament. 



2. General form and structure. 



a. In the animal now laid bare may be distingu ished — 

 a. A dorsal border turned towards the hinge of 

 the shell, and nearly straight. 



