VENUS 129 



(a) Filaments. Run the width of the gill. 



(b) Interfilamentar junctions. Form bridges connecting 

 the filaments. 



(c) Inhalant ostia. The openings bounded by filaments 

 and interfilamentar junctions. 



(d) The position of the torn interlamellar junctions, ap- 

 pearing as indefinite dark stripes running in the same direc- 

 tion as the filaments. 



With a high power observe: 



(a) The chitinous rods which lie inside of the filaments 

 and stiffen them. 



{b) The cilia on the sides of the filaments. These are of 

 two kinds: (1) surface cilia that form currents of water 

 along the filaments. These will be seen waving back and 

 forth, or if still moving rapidly, apparently moving along the 

 sides of the filaments. (2) Deeper cilia that are down be- 

 tween the filaments and can be seen by changing the focus. 

 These move at right angles to the others, and apparently 

 become longer and shorter. Explain. 



Draw a surface view of a piece of a lamella. 



Examine a piece of the gill of Mytilus for the above struc- 

 tures. In this form the interfilamentar junctions are small 

 and composed of modified cilia only, and the inhalant ostia 

 are correspondingly large. By pressing the gill the inter- 

 filamentar junctions can be pulled apart. 



Study prepared sections of the gill of Venus and notice: 



1. Lamellae. 



2. Interlamellar junctions. 



3. Water tubes. 



4. Filaments. 



5. Interfilamentar junctions. 



6. Cilia. 



7. Inhalant ostia. 



8. Blood spaces. 



9. Chitinous rods. 

 Draw. 



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