484 MONTGOMERY. 



might produce also a difference in the structure of the intestine, 

 and a different manner of procuring it might modify the pro- 

 boscis. Further, the action of different climatic influences, 

 especially the rapid cooling of the bodies of freshwater during 

 the winter, and the periodical cessation of active life caused by 

 this agency, would influence the reproductive periods of the 

 nemerteans, and perhaps also the development. What is 

 needed is a careful study of these questions ; and I would feel 

 amply repaid if this little paper would stimulate others to the 

 active study of the interesting problems involved in the change 

 from salt to fresh water, — to an investigation of the modifica- 

 tions of structure, and the agencies which have produced them. 

 And the results of such a study would naturally be of far more 

 use in the attempt to solve the problem of the inheritance of 

 acquired characters, than to experiment upon individuals kept 

 in confinement, by gradually decreasing the salinity of the 

 water. For the objection is justified, that in such experiments 

 the organism is placed in pathological conditions, and that the 

 experimenter is attempting to produce structural changes in a 

 very brief time, which are (perhaps always) produced by natural 

 agencies very gradually, and through long periods of time. 



Woods Holl, Aug. 5, 1895. 



