RI PRODUCTIVE CYCLE IX AXODOXTA IMBECILLIS. 93 



other forms occurs in epithelial "cysts" on the gills of fishes, 

 requires in this species only 7-10 days, as compared with a mini- 

 mum of 12 14 in Lampsilis anodontoides and L. litteola. Develop- 

 ment from tin- fertilized ovum to the fully formed glochidium 

 may occur in two weeks' time. 



The duration of the interval between reproductive cycles 

 varies from 2 or 3 days to 2 (or rarely 3 )weeks. 



It is reali/ed that more extensive observations would provide 

 material for more accurate determination of the duration of 

 various stages of this cycle and the possible changes in these time 

 relations during the fall and winter months. 



However, the data at hand does warrant the condition that 

 Anodonta imbecillis cannot properly be classed as a long term 

 breeder. Juveniles are discharged during the latter half "I" 

 August and first half of September and a new reproductive cyele 

 begins. Whether this cycle is repeated throughout the month- 

 when this species is listed as gravid is still to be determined. 



DISCUSSION. 



The possible correlation of the rapid rate of growth and the 

 early attainment of sexual maturity of Anodonta imbecillis with 

 the thin "paper shell" has already been mentioned. It is possible 

 that this short reproductive cycle may be correlated with these 

 factors. 



No attempt was made to determine whether self or cross fer- 

 tili/ation is the normal process in Anodonta imbecillis. Il >ell" 

 fertilization is the rule, hennaphroditism may h,i\c been .1 e<m- 

 tributing factor in the establishment of a shorter reprodm u\ t - 

 cycle. 



Since to date only two species have been reported as de\ eloping 

 aparasitically, the idea that they may h.i\ r depended .it one time 

 upon parasitic metamorphosis, but later e\ol\rd .in ability to 

 develop independently, seems natural. Many iiue-ti^ators 

 have commented on the existence of -null hook- at the valve 

 edges as constituting the remains of a former pa i a -i tic adapta- 

 tion. Since parasitism on fishes which make -ea-onal upstream 

 migrations furnishes an efficient method of di.-tril union (possibly 

 (he only method of extensive upstream migration of mussels), 

 a u ide distribution of aparasitic form- \\< mid lend added weight to 



