OBSERVATIONS ON PECTEN DISLOCATUS. 263 



closely to the bottom of the dish and after a short time, slowly 

 withdraw it, leaving a rather broad band of slightly yellowish 

 material attached to the glass and connected with the foot by the 

 byssal gland. This is not composed of small threads as in the 

 mussels mytihis and inodiola, but it may be sufficiently tough to 

 support the weight of the animal, if, after a few minutes, the dish 

 is carefully turned over." 1 



SUMMARY. 



By way of summary, therefore, it might be said concerning the 

 function of the notch that it makes possible a much freer use of 

 the foot and byssal gland, and is in some way connected with the 

 function of these organs. Although many mollusks live in the 

 mud, the fact that young Pectens do not is evidence that they do 

 better out of it. The foot and byssus enable them to climb upon 

 supports and maintain their position there. As they approach 

 maturity, they assume more and more the swimming habit and 

 the foot and byssus lose, to some extent or entirely, their func- 

 tional activity. If these organs are not functional in full-grown 

 Pectens, as seem probable, the notch is no longer of any value to 

 them, although it is not obliterated. 



The Pecten has the sense of position well developed. 



EARLHAM COLLEGE, RICHMOND, INDIANA, 

 March 6, 1909. 



1 The University of Maine Studies, No. 6, September, 1906, p. 18. 



