180 



SCIENCE. 



[N. S. Vol. II. No. 33. 



of life; but very little is written concerning 

 the methods by which species peculiar to 

 one locality may be transported to others 

 many miles distant. This is a subject 

 which bears more closely on the origin of 

 species than any other, and one which will 

 yield some of the best results, if studied 

 carefully and faithfully, and if original ob- 

 servations are made in the field. It is my 

 purpose in this communication to briefly 

 consider some of these transporting agen- 

 cies as illustrated bj' the Mollusca, from 

 facts gathered by myself while collecting in 

 the field, and from reliable correspondence. 



Distribution by the aid of birds. — Several 

 years ago, while on a collecting trip to 

 Florida, I took occasion to dissect several 

 hundred migrant and resident birds and to 

 carefully note the contents of their crops. 

 In a large number of the crops I found the 

 shells of mollusks which had been taken as 

 food; these shells were mostly minute, and 

 of the genera PiqM, Amnicola, Piddium and 

 Vertigo. These shells, being indigestible, 

 and not affected by the gastric juices of the 

 stomach, would naturally pass off with the 

 fffices. In this manner, the shells of many 

 species of mollusks, which were once sup- 

 posed to inhabit restricted localities, have 

 been found at a great distance from their 

 recorded habitats. Especially would this be 

 true during the migratory season , when a bird 

 would swallow a species in one State and 

 drop the shell with the fasces in another. 

 The shells, of course, would in most cases be 

 dead when dropped, the animal portion be- 

 ing used as food; but there are exceptions to 

 this, for I have several authentic accounts 

 of living mollusks being found in the stom- 

 achs of birds. As an example of the wide 

 distribution of these small mollusks, I cite 

 Pupa armifera, Say, which is found from 

 Dakota and Kansas to the Eastern States 

 and Mexico. 



The Catbird ( Galeoseojites carolinensis) I 

 found to feed only (so far as the Mollusca 



were concerned) on the minute land 

 snails Pupa and Vertigo. It was frequently 

 observed on the palmetto trees searching 

 for these minute animals. The hawks and 

 kites of Florida, especially the Everglade 

 Kite, seemed to consider the animal of Am- 

 pullaria depressa, Say, a great delicacy, for 

 in almost everj' crop dissected I found the 

 remains of this mollusk. Heaps of the dead 

 shells of this animal were always found be- 

 neath their roosting places. Frequently a 

 hawk or kite will capture this fresh-water 

 snail and carry it several miles to its roost- 

 ing place ; but many times another bird 

 will overtake the one carrying the booty, 

 and a dispute of ownership will follow, 

 which nearly always results in the loss of 

 the prey, which drops unharmed, j)erchance, 

 into a pond which this species has not before 

 inhabited, and there, if laden with eggs, as 

 is frequently the case, establishes a new 

 colony of Ampullaria. By this means, as 

 well as others, this species has been dis- 

 tributed over a great portion of Florida. 

 It is my belief that many a colonj^ of mol- 

 lusks, as well as other animals, has been 

 formed in this manner. 



Ducks, geese, swans and manj"- other 

 kinds of wild fowl, are very fond of snails, 

 and I have never failed to find the re- 

 mains of them in their crops. By means 

 of these birds the shells of many mollusks 

 have been transported for many miles, and 

 have offered, doubtless, material over which 

 some conchologist has worried and finally 

 described them as a new species ! I know 

 of several instances where the eggs of a 

 muUusk were found attached to the foot of 

 a mallard, and several birds have come 

 under my notice, which, when shot, had 

 young Anodons and Sphjcriums adhering to 

 their toes. Many other instances might be 

 cited of this character, but enough has been 

 said to show that birds exert a wide influ- 

 ence in the distribution of the mollusca. 



Distribution by the aid of fi.'<hes. — Various 



