A monograph of the Anopheles mosquitoes of India / by S.P. James and W. Glen Liston.

  • Sydney Price James
Date:
1904
Catalogue details

Licence: In copyright

Credit: A monograph of the Anopheles mosquitoes of India / by S.P. James and W. Glen Liston. Source: Wellcome Collection.

    82/238 (page 60)
    Definition of species. That this must be so is shown by the occasional appearance of monstrosities,” which differ markedly from their progenitors, but which cannot be classed as belonging to a different species because they are incapable of handing down to succeeding genera- tions such abnormal differences. By many authorities a third defining limit has been applied to the term “ species.” They believe that true species, when intercrossed, are often sterile, and, when fertile, the hybrids produced are almost always sterile. Varieties, on the other hand, are almost always fertile. The idea of species, then, must rest on three orders of facts : (1) the morphological resemblances between individuals; (2) the lineal transmission of distinctive characters ; and (3) the sterility of first crosses between species or their hybrids. Although the practical application of this definition of species is involved in many difficulties, we may reasonably expect that some attempt to conform to it should be made by naturalists. It is well known that entomologists are particularly neglectful in this respect, and that they have recorded a vast number of forms as distinct species on the strength of single specimens and without any know- ledge of their generation. In the large majority of cases the species of mosquitoes have been established solely on the morphological characters of dead specimens. We think it is not unreasonable to expect that before an entomologist decides to class any mosquito as the representative of a new species, or a new genus, he should consider whether it represents merely an “individual difference,” a “ monstrosity ” or a “ variety.” To workers in India it is well known, for example, that the different individuals hatched out from the same batch of mosquito eggs vary greatly in size, and we have found that the adults developed from any batch of eggs of A. cidicijacies can almost always be readily divided into a group of large and a group of small individuals. Yet size is a character not infrequently relied upon by Mr. Theobald for the separation into distinct species of two mosquitoes alike in other respects. His species Myzomyia minutus. for example, which was described from a single specimen forwarded to him from Lahore, would appear to have been founded upon this character alone, and the same character is used as one of the points of distinction between A. funestus and A. rhodesiensis. Under the heading of “ individual differences ” comes also the question 6o]