354 THE ZOOLOGIST 



colour production in insects is dependent on the action of a group of 

 closely related enzymes, of which chitase, the agent which produces 

 hardening of chitin, is the most important, Tower demonstrates by a 

 series of well-planned experiments that colours are directly modified 

 by the action of external agencies— viz. temperature, humidity, food, 

 altitude, and light. Food chiefly affects the subhypodermal colours 

 of the larvae, and does not enter much into account ; the most im- 

 portant agents affecting the adult coloration being temperature and 

 humidity. A slight increase or a slight decrease of temperature or 

 humidity was found to stimulate 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 proposition that induced somatic changes are not 

 inheritable. 



But it was found necessary to remove the individuals experi- 

 mented upon from the influence of changed conditions during the 

 periods of growth and maturation 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 develop- 

 ment 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 

 imagos to experimental conditions during the development of some 

 of the batches of ova and to normal conditions during the develop- 

 ment 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 pressure, during the development 

 and fertilization of the first three batches of eggs. Such conditions 

 had been found productive of albinic deviations in previous experi- 

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

 conditions, and the larvae 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 decemlineata. 

 This gave a clear indication that the altered conditions had produced 

 modifications in the germ-cells which were expressed by colour 



