48 Lake Maxinkuckee, Physical and Biological Survey 



of mussel food are by no means exhaustive, but represent hurried 

 examinations and a record of the more easily recognized forms 

 out of a mass of doubtful material. They are intended to be simply 

 suggestive. 



Closely connected with the question of food and nutrition is that 

 of the size of mussels. A marked feature of the mussels of Lake 

 Maxinkuckee as well as of the neighboring lakes, is the dwarfing 

 of many of the species, and this is rather difficult to explain, when 

 one considers the large amount of organic material they ingest. 

 The mussels of a few northern lakes examined were thick-shelled 

 and large, so this dwarfness may not be necessarily associated with 

 lake conditions, that is, absence of current. A possible explana- 

 tion is that of close inbreeding, 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, reproduction, etc.: The reference to inbreed- 

 ing 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 fe- 

 males of the mussels of lakes and rivers during the proper seasons ; 

 but the general impression gained from having examined the mus- 

 sels of numerous lakes and rivers through the different seasons is 

 that there are fewer of the mussels of the lake that succeed in hav- 

 ing their ova fertilized. Gravid mussels are indeed not rare in the 

 lake at the 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 characteristic female 

 form but only 25 were gravid. Likewise of 18 Anodontas exam- 

 ined on the same date, only 2 were gravid. This is a considerably 

 lower percentage than one would expect in rivers at that 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 spawning season certain species of mussels, especially Lamp- 

 silis ventricosa, and L. multiradiata, exhibit, in the neighboring 

 rivers, a very striking appearance, due to the excessive develop- 

 ment 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 crowded 

 beds, moreover, one frequently encounters precocious individuals; 

 small shells, usually apparently only two or three years old but 

 gravid and with the characteristic female contour markedly de- 



