259 



considers the large amount of organic material they ingest. The mus- 

 sels of a few northern lakes examined were thick-shelled and large. 

 So this dwarfing may not be necessarily associated with lake conditions, 

 that is, absence of current. A possible explanation is that of close in- 

 breeding, there being no admixture of new blood with other distant 

 colonies, such as is possible where the lake is in close connection with 

 a large river and its mussel beds. 



Breeding Habits, Rejjroduction, etc. — The reference to inbreeding 

 above leads to a consideration of breeding and breeding habits. At first 

 glance it would appear that lakes, having no, or only feeble, currents, 

 would make fertilization of the ova of the female mussels largely a 

 question of chance. It is not possible, with the data at hand, to make 

 precise comparisons between number of gravid females of the mussels 

 of lakes and rivers during the proper seasons, but the general impression 

 gained from having examined the various mussels of numerous lakes and 

 rivers through the different seasons is that there are fewer of the 

 mussels of the lake that succeed in having their ova fertilized. Gravid 

 mussels are indeed not rare in the lake at proper seasons, but they 

 seem to be much fewer than one might expect. On October 17, 1907, 

 for example, of 252 Lampsilis luteola examined, 41 were of the charac- 

 teristic female form but only 25 were gravid. Likewise, of 18 Ano- 

 dontas examined on the same date, only 2 were gravid. This is a con- 

 siderably lower percentage than one would expect in rivers at this date. 

 There are other indications that the functions of reproduction are much 

 less prominent in the lake than in rivers. In the height of the spawn- 

 ing season certain species of mussels, especially Lampsilis ventricosa 

 and L. multiradiata, exhibit, in the neighboring rivers, a very striking 

 appearance, due to the excessive development and high coloration of 

 portions of the mantle near the inhalent aperture. Though both these 

 species are found in the lake, none was observed in this condition. In 

 some rivers in densely crowding beds, moreover, one frequently en- 

 counters precocious individuals; small shells, usually apparently only 

 2 or 3 years old but gravid with the characteristic female contour mark- 

 edly developed. This is possibly related to opportunities of fertiliza- 

 tion of ova, and is most frequently observed in L. ventricosa and L. 

 luteola. No such precociously developed mussels were found in the lakes. 



A large and well developed female Lavij)silis ventricosa was trans- 



