Vol. LXII, No. 3 June, 1932 THE BIOLOGICAL BULLETIN PUBLISHED BY THE MARINE BIOLOGICAL LABORATORY A STATISTICAL TEST OF THE SPECIES CONCEPT IN LITTORINA JOHN COLMAN MUSEUM OF COMPARATIVE ZOOLOGY, HARVARD UNIVERSITY "One may believe that if larger series were more often utilised in taxonomic work the current bewilderment over variation would give way to a renewed respect for a certain uniformity that exists thruout such groups of individuals." Kinsey. With certain exceptions, no two individuals of a species are ever genetically identical; hence it is not so much the uniformity as the character and range of variation in a species that are diagnostic. Conversely, the fact that two related animals differ does not necessarily mean that they belong to separate species unless it can be shown, after the examination of sufficient numbers collected over a wide area, that there is not a series of overlapping intergrades between the two differing forms. It was, for example, the range in variation in the number of vertebrae in conger eels that enabled Johannes Schmidt (1931) to separate the American species, Conger oceanicus, from the European C. mdgaris. The ranges of the larvae of the two species overlap in part geographically, but not anatomically, the number of vertebras in C. oceanicus being from 140 to 149, average 144.63, and in C. vulgaris from 154 to 163, average 158.16. This lack of overlap in the numbers of their vertebrae clearly justifies their segregation. Kinsey (1930) has shown, too, that the highly variable Gall Wasp, Cynips erinaceus, is one species, though extreme forms of its gall have been previously assigned to separate species. In any part of its wide range a comprehensive collection over a square mile will very closely resemble a similar comprehensive collection at any other place in the insect's range. The variation in the species is roughly constant throughout its entire geographic range. These are two extreme cases; the first of two distinct, the second of one homogeneous, species. If, however, the two conger eels had 15 223
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