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A new and novel approach to the problem of speciation in 

 Thais populations is in the publication by Dr. Hansrudolph 

 Staiger (1954, 1955) of two papers dealing with the differen- 

 tial genetic organization of local races o( Thais lapillus. In his 

 first paper entitled '* Der Chromosomendimorphismus bcim 

 Prosobranchier Purpura lapillus in Beziehung zur Okologie 

 der Art " Dr. Staiger gives an account of his genetic studies 

 of a group of local races o( lapillus, some forty-eight in num- 

 ber, found upon the coast of Brittany in Northern France. 

 However, all but seven of the populations were derived from 

 a rather limited area in the vicinity of Roscoff and the Bay of 

 Morlaix, about twenty-two kilometers in cross-section, but 

 with a wide range of ecological stations admirably disposed 

 for the purpose of this study. Dr. Staiger does not give us 

 any figures or detailed descriptions of the snails found in the 

 local populations, the principal point emphasized being the 

 relative thickness of the shell. From this we assume the prob- 

 lem was not complicated by factorial conditions involving 

 coloration and sculpture. 



As the result of his investigation of the cytological condi- 

 tions in hundreds of specimens of the localized races o( lapillus 

 Staiger was enabled to determine that the heredity of this 

 species is governed by a group of chromosomes which vary in 

 number from 13 t(j) 18. Of these 8 are present in the germ-cells 

 of all individuals, and form the basic hereditary elements; the 

 remaining group of chromosomes in six possible combinations 

 providing for the diversities characteristicof local races of poly- 

 typic forms. The accompanying diagram, copied from the 

 Staiger monograph, will give a graphic interpretation of the 

 chromosomal organization. The eight basic or central chromo- 

 somes, technically termed acrocentric or metacentric, are num- 

 bered from 1-8; the group involved in initiating changes of 

 a polymorphic character are numbered I-V. 



While the acrocentric chromosomes are regarded as the 

 more conservative elements in the hereditary complex, they 

 may also play a part in initiating polymorphism, but their 

 influence is not so readily determined. 



