j6 SMITHSONIAN INSTITUTION 



of the noddy terns, which formerly made their nests in trees or shrubs. 

 This summer all had changed to a ground-dwelling habit. Still re- 

 taining the desire to make nests, they gathered bits of dead twigs and 

 shaped them into a semblance of a nest upon the ground. They ap- 

 pear to have a decided ligno-tactic sense, for old boards seem to satisfy 

 the desire for wooden homes, and birds were found incubating their 

 eggs placed upon bare boards. All but one nest was on the ground, 

 the exception being a nest placed in the single remaining young 

 coconut. 



Bird Key has been reduced to about half its former size by wind and 

 waves, and the warden's house, which some years ago was trans- 

 ported from the west side to the center of the island, has been de- 

 stroyed, the roof now resting upon the ground. This marks the en- 

 croachment of the sea, which has eaten away the western half of the 

 island. 



Figures ~]2 and /$ show glimpses of conditions as they obtained 

 this summer. They should be compared with the illustrations in the 

 paper referred to above. 



CERION COLONIES 



Prior to my experiments with Cerion breeding, it was generally 

 held that these land mollusks were very plastic and readily responded 

 to annual differences in environment ; for example, it was held by 

 some that a dry year might produce a dwarf progeny, a wet year with 

 its more luscious vegetation, the opposite, and that the many forms 

 which characterize the Bahamas, for example, might best be consid- 

 ered merely responses to temporary environmental conditions. Our 

 breeding experiments have already determined that the Bahaman 

 Cerions require three years to attain maturity, and the West Indian 

 four, which eliminates the seasonal effect. All our experiments to 

 date, with one exception, have shown that during the interval of our 

 experimentation, the various generations produced under the changed 

 environmental conditions, and these are many, have produced no 

 recognizable changes in the progeny of the different generations. Our 

 hybridization experiments, on the other hand, have brought to light 

 what I believe to be the basis of mutation. In both of the instances re- 

 ported here and elsewhere where we have crosses of unrelated species 

 an enormous number of mutants have appeared in the second genera- 

 tion, paralleling such observations as have been noted for Lamarck's 

 evening primrose and the fruitflies. I have elsewhere recorded a simi- 

 lar state of affairs for the genus Cerion, which I have found taking 

 place in nature without the intervention of man. 



