REPRODUCTIVE CYCLE IX ANODONTA IMBECILLIS. 89 



\v-re made at intervals of several days on more than one hundred 

 individuals. This has furnished the following evidence for a 

 shorter reproductive cycle than formerly reported for thi- -pecies. 



MATERIAL AND METHOD. 



Anodnnla imbecillis is commonly called the "paper shell " 

 because of the extreme thinness of the valves. Pos>ibly corre- 

 lated with this economy in shell formation, is its rapid rate of 

 growth. It may begin to reproduce during the second year. The 

 observations in this paper were made on two- and three-year-old 

 mussels. 



In this species the outer gills serve as marsupia. It i> an easy 

 matter to insert a capillary pipette between the valve-, mak 

 HMjJe puncture in the marsupium, and remove some of it- con- 

 tents with only slight injury to the mussel. This puncture In 

 rapidly. In order that the least possible modification of reproduc- 

 tive activity might be produced by this examination, tin- >am 

 removed were small, containing only from 20 to 40 individual-;. 

 The puncture was made in a direction parallel to the loni; a\i- <>t 

 the gill so that the sample removed contained young from several 

 v;ill compartments. 



Relatively slight disturbances may cause "abortion "'of mar- 

 supial contents in some species. Lefevre and Curtis, however, 

 note that they have never observed abortion in Anodonta. The 

 thin shell of .1. imbecillis renders the above described operation 

 very simple as the valves may be opened for the insertion of the 

 pipette with the thumb nails. This probably eliminate- the 

 possibility of abortion as a factor bearing upon the folloxvin- 

 evidence. 



The examinations extended over a period of one and one half 

 months from the middle of July to early in September. 



Most of the mussels studied were taken from the main supply 

 reservoir of the V. S. Fisherie- Hiolo-jc.il Station at Fairport, 

 Iowa, which is supplied daily from the Mi i--ippi River. A few 

 preliminary observations were made on mus^el> taken from the 

 river. 



Throughout the observations they were kept in running water 

 in experimental troughs supplied from a pond containing an 

 abundance of pond life. As opportunity for considerable sedi- 



