September 22, 1910J 



NATURE 



stimulate the action of the colour-producing enzymes, 

 giving'd tendency to melanism; but a large increase or 

 decrease of temperature or humidity was found to inhibit 

 the action of the enzymes, producing a strong tendency to 

 albinism. 



A set of experiments was undertaken to test the question 

 whether colouration changes induced by changed environ- 

 mental conditions were inherited, increased, or dropped in 

 successive generations. These experiments, carried on for 

 ten lineal generations, showed that the changed conditions 

 immediately produced their maximum effect ; that they 

 were purely somatic and were not inherited, the progeny 

 of individuals which had been exposed to changed con- 

 ditions through several generations promptly reverting 

 when returned to normal conditions of environment. So 

 far the results are confirmatory of the well-established 

 proposition that induced somatic changes are not inherit- 

 able. 



But it was found necessary to remove the individuals 

 experimented upon from the influence of changed conditions 

 during the pl'nods of growth and maturation of the germ- 

 cells. Potato-beetles emerge from the pupa or from 

 hibernation with the germ-cells in an undeveloped con- 

 dition, and the ova do not all undergo their development 

 at once, but are matured in batches. The first batch 

 matures during the first few days following emergence, 

 then follows an interval of from four to ten days, after 

 which the ne.xt batch of eggs is matured, and so on. This 

 fact made it possible to test the effect of altered conditions 

 on the maturing germ-cells by subjecting its imagos to 

 experimental conditions during the development of some of 

 the batches of ova and to normal conditions during the 

 development of other batches. 



In one of the experiments four male and four female 

 individuals of L. decemlineata were subjected to very hot 

 and dry conditions, accompanied by low atmospheric pres- 

 sure, during the development and fertilisation of the first 

 three batches of eggs. -Such conditions had been found 

 productive of albinic deviations in previous experiments. 

 As soon as the eggs were laid they were removed to normal 

 conditions, and the larva; and pupae reared from them were 

 kept in normal conditions. Ninety-eight adult beetles were 

 reared from these batches of eggs, of which eighty-two 

 exhibited the characters of an albinic variety found in 

 nature and described as a species under the name pallida ; 

 two exhibited the characters of another albinic species 

 named iivinaculothorax^ and fourteen were unmodified 

 decenilincatas. This gave a clear indication that the 

 altered conditions had produced modifications in the germ- 

 cells which were expressed by colour changes in the adult 

 individuals reared from them. To prove that the devia- 

 tions were not inherent in the germ-plasm of the parents, 

 the latter were kept under normal conditions during the 

 periods of development and fertilisation of the last two 

 batches of eggs ; the kirva^ and pupae reared from these 

 eggs were similarly subjected to normal conditions, and 

 gave rise to sixty-one unmodified decemlineatas, which, 

 when bred together, came true to type for three genera- 

 tions. The decemlineata forms produced under experi- 

 mental conditions also came true to type when bred to- 

 gether. Of the pallida forms produced by experimental 

 conditions all but two males were killed by a bacterial 

 disease. These two were crossed with normal decemlineata 

 females, and the result was a tvpical Mendelian segregation, 

 as shown by the following table : — ■ 

 2 d pallida x 2 9 de 



Hybrids, decemlir 



I characters dominant 



Decemlineata and hybri 

 16 S. I* ? 



Pallida Pallida Decemlineata and hybrids 



18 <J,23 ? S 6,7 9 26 <J,28 9 



This is a much more detailed experiment than those of 

 NO. 2134, VOL. 84] 



Standfuss, Merrifield, and Fischer, and it shows that the 

 changes produced by the action of altered conditions on 

 the maturing germ-cells were definite and discontinuous, 

 and therefore of the nature of mutations in De Vries' 

 sense. 



In another experiment Tower reared three generations 

 of decemlineata to test the purity of his stock. He found 

 that they showed no tendency to produce e.xtreme varia- 

 tions under normal conditions. From this pure stock 

 seven males and seven females were chosen, and subjected 

 during the maturation periods of the first two batches of 

 ova to hot and dry conditions. Four hundred and nine 

 eggs were laid, from which sixty-nine adults were reared, 

 constituted as follows ; — 



Twenty (12 <J, 8 9) . . appartnily normal itof;«//nfa^a. 



Tweniy-lhree (10 <S , 13! 9) ■ {•<illMii- 



Five (2 i, 3 9) ■ ■ ■ iinmacniotho.ax. 



Sixteen l^ (i, 7 9) . • '•^^'■''''■ 



These constituted lot \. 



The same seven pairs of parents subjected during the 

 second half of the reproductive period to normal condi- 

 tions gave 840 eggs, from which were reared 123 adults, 

 all decemlineatas. These constituted lot B. The decem- 

 lineatas of lot A and lot B were reared side by side under 

 normal and exactly similar conditions. The results were 

 striking. From lot B normal progeny were reared up to 

 the tenth generation, and, as usual in the genus, two 

 generations were produced in each year. The decem- 

 lineatas of lot A segregated into two lots in the^ second 

 generation. A' were normal in all respects, but A', while 

 retaining the normal appearance of decemlineata, went 

 through five generations in a year, and this for three 

 successive years, thus exhibiting a remarkable physio- 

 logical modification, and one without parallel in nature, 

 for no species of the genus Leptinotarsa are known which 

 produce more than two generations in the year. Ihis 

 experiment is a sufficient refutation of Weismann's argu- 

 ment that the inheritance of induced modifications in 

 Vanessa tirticae is only apparent, the phenomena observed 

 being due to the inheritance of two kinds of determinants 

 — one from dark-coloured forms which are phyletically the 

 oldest, and the other from more gaily coloured forms 

 derived from the darker forms. 'Ihere is no evidence 

 whatever that there was ever a species or variety of potato- 

 beetle that produced more than two, or at the most, and 

 then as an exception, three broods in a year. 



The modified albinic forms in this last experiment of 

 Tower's were weakly; they were bred through two or 

 three generations, and came true to type, but then died 

 out. No hybridisation experiments were made with them, 

 but in other similar experiments, which I have not time 

 to mention in detail, modified forms produced by the action 

 of changed conditions gave typical Mendelian characters 

 when crossed with unmodified decemlineatas, thus proving 

 that the induced characters were constant and heritable 

 according to the regular laws. 



I have thought it worth while to relate these experi- 

 ments at some length, because they seem to me to be very 

 important, and because they do not appear to have 

 attracted the attention in this country that they deserve. 



They are confirmed to a very large extent by the experi- 

 ments of Prof.' Klebs on plants, the results of which were 

 published this summer in the Croonian Lecture on 

 '■ .iterations of the Development and Forms of Plants as 

 a Result of Environment." As I have only a short 

 abstract of the Croonian Lecture to refer to, I cannot say 

 much on this subject for fear of misrepresenting the 

 author ; but, as far as I can judge, his results are quite 

 consistent with those of Tower. Sempervivum funckit 

 and S. acuminatum were subjected to altered conditions of 

 light and nutrition, with the result that striking varia- 

 tions, such as the transformation of sepals into petals, of 

 petals into stamens, of stamens into petals and into 

 carpels, were produced. Experiments were made on 

 Semper-iiivum acuminatum with the view of answering the 

 question whether such alterations of flowers can be trans- 

 mitted. The answer was in the affirmative. The seeds of 

 flowers artificially altered and self-fertilised gave rise to 

 twentv-one seedlings, among which four showed surprising 

 deviations of floral structure. In two of these seedlings 



