1889.] NATURAL SCIENCES OF PHILADELPHIA. 347 



The following' communications were made in connection with the 

 proceedings of the Biological and Microscopical Section : 



Activity in Donax. — Dr. Benjamin Sharp described an interest- 

 ing case of activity in a bivalve studied by him on the beach of the 

 island of Nevis, B. W. I. Noticing some active little animals in the 

 swash of the breakers, he took them at first sight to be a form of 

 Crustacea. He had some difficulty in catching them and to his sur- 

 prise found them to be a species of Donax. When they wished to 

 flee from a real or supposed cause of danger, they protruded more 

 than half their length from the sand, as the breakers receded. Those 

 that were not carried into the deeper water on becoming exposed to 

 the air by the retreating waves, buried themselves with astonishing 

 rapidity in the sand and waited for the swash to again flow over 

 them, not protruding themselves until the current returned. The 

 method of getting up the beach was just the reverse of the 

 former action ; that is, they protruded after the receding water had 

 left them dry, so that the "up-shoot" carried them up the slope. 

 A.S soon as the water began to recede they anchored themselves 

 and disappeared into the sand rapidly, waiting thus until the 

 approaching wave came to help them again, and so on. The 

 power of appreciating the shock caused by the breaker on the sand, 

 and also the approach of footsteps, the power of recognizing quickly 

 the direction of the current and how to utilize it in avoiding danger, 

 and the ability to place themselves in a more congenial position on 

 the beach, were indicated by these actions. Did they depend on the 

 sense of hearing? These bivalves exist in enormous numbers on the 

 beach, which actually bristled with them when they protruded. 

 They were of all. sizes, from exceedingly minute specimens to those 

 a half an inch or more in length. 



( 'hange of habit causing change of structure. — Dr. Benjamin Sharp 

 also made some remarks on the Flicker or Ground Woodpecker, 

 Colaptes auratus, his attention having been called to the subject by 

 an amateur ornithologist. Air. Long, now of Nantucket. 



It is well-known to ornithologists that the flicker has departed 

 from the typical habits of the woodpecker in a number of ways. 

 It feeds on insects, especially ants, taken from the ground in prefer- 

 ence to the laborious method of excavating them from under the bark 

 of trees or from decaying wood, and in making its nest it selects a 

 hollow tree, rather than make the effort of boring out a new cavity 

 in the solid wood. The popular name, "Ground Woodpecker," 

 indicates, to a certain extent, the divergence from the woodpecker's 

 habits. 



When the bird is examined it will be found that the bill is weaker 

 than is usual in this group of birds, and that it is curved more or 

 Less in different specimens, showing a considerable amount of varia- 

 tion. If this curve increases it will soon become impossible for the 

 bird to use it as a drill except in soft substances. The feet in this 



