220 PROBLEMS OF GENETICS 



beetles which the author has observed and bred in many parts of 

 their distribution throughout the United States, Mexico and 

 Central America. The part of the book which has naturally 

 excited the greatest interest is that in which Tower states that 

 by subjecting the beetles to change in temperature and moisture, 

 he caused them to produce offspring quite unlike themselves, 

 which in several cases bred true. 



It is much to be regretted that the author did not happen to 

 become acquainted with Mendelian analysis at an earlier stage 

 in the investigation. The evidence might then have been 

 handled in a much more orderly and comprehensive way, and a 

 watch would have been kept for several possibilities of error. 



The headquarters of the genus is evidently as Tower states, 

 in Mexico and the adjoining countries. In this region there is 

 a great profusion of forms, some very local, some as for instance 

 the well-known decemlineata, 8 more widely spread. The dis- 

 tinctions are almost all found in peculiarities of colour and 

 pattern, and the limits of species are even more indefinable than 

 is usual in multiform animals. Tower arranges the various types 

 into seven groups of which the one most studied is that which 

 he calls the lineata group. To this group belong all the forms 

 to which reference is here made, and, as I understand, they differ 

 among themselves entirely in size, colour and pattern. There 

 is no suggestion of infertility in the crosses made between the 

 several forms of the lineata group; in fact they present, like many 

 Chrysomelidae, a good example of what most of us would now 

 call a polymorphic species, consisting of many types, some found 

 existing in the same locality, others being geographically isolated. 



A series of experiments was devoted to the attempt to fix 

 strains corresponding to the extremes of continuous variations. 

 For example, those with most black pigment and those with 

 least black taken from a population continuously varying in this 

 respect, were separately bred; but almost always the selection 

 led to no sensible change in the position of the mean of the popu- 



8 This is the famous Colorado beetle or potato-bug, which has caused such serious 

 destruction in potato crops. There seems to be no doubt that this insect, formerly 

 unknown in the eastern States, made its way east along the mining trails when the 

 west was opened up. 



