July 19, 1907] 



SCIENCE 



73 



was at its greatest, several mutations were 

 produced. 



Thus there were produced from the light 

 (dry) series examples of pallida and defecto- 

 punctata, and from the dark (wet), specimens 

 of melanicum. The most mmierous of these 

 was the pallida, a form with the usual mark- 

 ings, but the ground color exceedingly pale. 

 This pallida occurred also out of doors in the 

 potato fields, but so rarely that Professor 

 Tower is convinced that it is virtually impos- 

 sible for it to establish itself. When isolated 

 and inbred, however, it comes perfectly true, 

 and in this way a very numerous colony of 

 pure pallida was obtained. Some of these 

 were bred in company with typical decem- 

 lineata, and it was found that the normal 

 crossings (i. e., of like beetles) were to the ab- 

 normal as Y to 1. On account of this, the 

 pallida were not swamped, but continued to 

 increase when both were transferred to natural 

 conditions in the grounds of the University of 

 Chicago. Professor Tower was very anxious 

 to allow the pallida to spread widely over the 

 country, and see what would happen; but the 

 injurious character of the insect made this 

 impossible and so the colony was destroyed. 



When bred with decemlineata, pallida gave 

 the normal Mendelian results, with decem- 

 lineata dominant. 



Melanicum, the dark variety, is in some 

 ways even more interesting. 



It appears to be very distinct, and is crossed 

 with difficulty with decemlineata; when a suc- 

 cessful cross is obtained, the results are Men- 

 deli an. 



It is, moreover, ill adapted to the habitat of 

 decemlineata, into which it must be born, as it is 

 apparently able to live or reproduce only in a 

 high percentage of humidity. My experience with 

 them is that only the above condition can be used 

 for their propagation in experiment, and there is 

 every reason to believe they would require a like 

 condition in nature. 



This appears to be very suggestive of a 

 method of origin of a new species. It is 

 shown that the mutation melanicum arises 

 from decemlineata when the latter is subjected 

 to conditions of moisture, and that it requires 



excessive moisture. Let decemlineata reach 

 a too moist region, and produce a few melani- 

 cum; will not these proceed still farther into 

 the humid area, and there multiply in comfort 

 and isolation, forming a veritable new species ? 

 This will be facilitated by the difficulty of 

 crossing with the parent form. 



Chapter IV., on habits and instincts in 

 Leptinotarsa, is especially important for the 

 understanding of the evolution of these beetles. 

 It was ascertained that selective mating ex- 

 isted in respect to size, being due to the in- 

 ability of abnormal individuals to properly 

 perform the sexual act. 



We do not ordinarily realize how narrow are 

 the limits within which successful copulation can 

 take place in insects, or how slight a variation 

 is sufficient to prevent the performance of the 

 sexual act with such completeness as to insure the 

 leaving of progeny. 



Nevertheless, as was to be expected, there 

 was no trace of psychological selection. 



The above account does not in any sense do 

 justice to this remarkable work. There is 

 much in it to which no reference has been 

 made; and I do not attempt a summary of 

 Professor Tower's closing chapter, which 

 should be read in its entirety, and is too long 

 to republish here. There are places where 

 one does not feel quite sure that the facts 

 justify the conclusions reached, and here and 

 there we find inconsistencies. We also regret 

 the absence of information in several places; 

 thus we are told that the conditions at Cabin 

 John Bridge were such as to produce many 

 mutations, but just what those conditions were 

 does not appear. We also have names for 

 some new species and varieties, without any 

 descriptions. These things, as I learn from a 

 letter received from the author, will be reme- 

 died in a subsequent publication; the present 

 volume (though of 320 pages) being merely 

 preliminary, and representing a mere fraction 

 of the whole material gathered. 



A rumor has reached me that there is some 

 question about the continuance of the grants 

 upon which Professor Tower's work depends. 

 This work is necessarily somewhat expensive; 

 but if, in some way or another, this country 



