REPK<>M I I VI-: CYCLE IX AXODOXTA IMBECILLIS. QI 



The com lu-ion drawn is that the reproductive season of 

 A notion/a inibcrillis in this location begins during the latter part 

 of July. 



As the-e observations were continued the various stages of 

 embryonic development and glochidial metamorphosis were 

 ideniilied and data accumulated as to the time required for this 

 transition. Eleven different stages were identified as follow- : ! 



1. Karly segmentation of the fertilized ovum. 



2. Later segmentation. 



3. Karly differentiation of the single anlage of the valves which 

 at this stage caps the segmenting cell mass. 



4. Formation of a groove in this "cap" which di\i<le- ii into 

 two separate valve anlagen. 



5. The developing valves lie on the segmenting cell mass "like 

 continents in relief on the globe." 



6. The two valves resemble a folded leaf which now completely 

 encloses the future "soft parts" of the young larva. 



7. The glochidial shape is attained but the larva is still color- 

 less and transparent. The single glochidial adductor muscle 

 can be seen to quiver or "Hash" although the valves are closed. 



N. The glochidia are now fully formed, have a rich \ello\v 

 color, and a single adductor muscle. Main- may be seen to 

 snap vigorously if freed from the egg membranes in the process 

 of removal from the marsupia. Those within the nn-inbranes 

 ha\e lln-ir valves opened. This stage is equivalent to that at 

 \\liich tin- glochidia of species dependent on para-it i-in on !i-h< - 

 for metamorphosis are extruded from the mar-upia. 



9. Mid-metamorphosis; rich yellow in color, no adductor 

 muscle visible. 



10. Late metamorphosis; the two delinir.xe adductor nni-< les 

 are now visible. Snapping of the v,il\<- cannot be induced by 

 freeing the glochidia from their e^ iiu-inbr.ii 



i i . Juvenile mussels; the foot i- m>\v visible, active -napping of 

 the valves and extension of the foot occui 



1 Xo attempt was made to describe fully tin- van pment; 



they are merely i haia. t> -ri/rd for greater accuracy in determining tin- duration of 

 developmental stages. Examination \va- made with a luno. ular mi> : "iag- 



nit'yinj; X 50. 



