624 TRANSACTIONS OF SECTION P. 



the action of the colour-producing enzymes, giving a 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 coloration 

 changes induced by changed environmental 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 conditions through 

 several generations promptly reverting when returned to normal conditions of 

 environment. So far the results are confirmatory of the well-established pro- 

 position that induced somatic changes are not inheritable. 



But it was found necessary to remove the individuals experimented upon from 

 bhe influence of changed conditions during the periods of growth and matura- 

 tion of the germ-cells. Potato-beetles emerge from the pupa or from hibernation 

 with the germ-cells in an undeveloped condition, 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 next 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 images 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. decem- 

 lineata were subjected to very hot and dry conditions, accompanied by low 

 atmospheric pressure, 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 larvie 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 immaculothorax, and fourteen were unmodified 

 decemtineatas. This gave a clear indication that the altered conditions had pro- 

 duced modifications in the germ-cells which were expressed by colour changes in 

 the adult individuals reared from them. To prove that the deviations 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 larvae and pupse reared from these eggs were similarly sub- 

 jected to normal conditions, and gave rise to sixty-one unmodified decemlineatas, 

 which, when bred together, came true to type for three generations. The decern- 

 lineata forms produced under experimental conditions al.so came true to type when 

 bred together. 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 typical Mendelian segregation, as 

 shown by the following table : — 



2 6* pallida X 2 9 decemlineata 



I 

 Hybrids, decemlineata characters dominant 

 5 <J x 3 ? 



Pallida Decemlineata and hybrids 



6 o, 4 9 If, <?, 14 ? * 



\ 



Pallida Pallida Decemlineata and hybrids 



18 6*, 23 9 8 6*, 7 9 26 <?, 28 ? 



