﻿NO. 5 SMITHSONIAX EXPLORATIONS, I922 45 



HEREDITY EXPERIMENTS IX THE TORTUGAS 



Dr. Paul Bartsch, curator, division of mollusks in the INIuseum, 

 has continued his heredity studies, for which molkisks of the genus 

 Ccrioji are used as a basis. He visited the various colonies trans- 

 planted to the Florida Keys from the Bahamas, Curacao, and Porto 

 Rico and made a. careful study of the new generations which have 

 arrived since last year. He reports a loss of all the material which 

 was placed in cages last year for the purpose of studying the crossing 

 products of selected pairs. A little experimenting led him to believe 

 that this loss was due to the fact that the fine screen ?\Ioncl wire used 

 for the cages, which not only covered the sides but also tops of these 

 structures, prevented dew formation on the vegetation in the inside 

 of the cages and thus inhil)ited the moisture required by these organ- 

 isms. A heavy dew forms at the Tortugas during the night, the time 

 during which Cerions are actively foraging for food, which is largely 

 gained by plowing immediately below the surface for fungal mycelial 

 threads. It is more than likely that the lack of dew also prevented 

 the proper formation of mycelia in the area enclosed by the wire 

 meshes and the Cerions may therefore not only have been famished 

 for want of water, but likewise starved. 



Dr. Bartsch believes that these were the controlling factors for he 

 found that by placing a piece of IMonel wire over a board at some 

 little distance from the board and leaving a portion of the same board 

 uncovered, the part over which the wire was stretched was found dry 

 in the morning, while the uncovered portion was duly covered with 

 moisture. To overcome this all the tops of the cages were removed 

 and a narrow fringe of wire, turned down at the distal edgQ, was 

 placed around each to prevent the Cerions from escaping. The cages 

 were then stocked with the same elements used a year ago. 



Two additional cages were built. The sides and top of one were 

 covered with paraffine treated cheesecloth and in the other the sides 

 only were covered with this material. In these, specimens were placed 

 in order to make sure that the contentions expressed above were the 

 active factors in the killing ofif of last year's material, and that the 

 attaching of the Cerions to the wire mesh of the sides of the cages, 

 which become decidedly warm when the sun shines upon them, was 

 not responsible. 



The Newfound Harbor hybrid colony was found flourishing. A 

 lot of dead specimens was brought to Washington for record. 



Two new mixed colonies were established, consisting of 500 Florida 

 grown specimens of Cerion viaregis Bartsch taken from Colony E, 



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