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undertaken by Tower, there are some which have a direct 

 bearing on the matter under consideration. Of these I propose 

 to give a brief account. It should be premised that the 

 beetles of the genus Leptinotarsa lay their eggs in batches, 

 each batch being laid before the next begins development. 



Experiment 1. — Males and females of L. decemlineata were 

 exposed to extremely hot and dry conditions, accompanied by 

 low atmospheric pressure, daring the growth and fertilisation 

 of the first three batches of ova. These were reared from the 

 outset in normal conditions. Out of 96 specimens so obtained, 

 82 were of the varietal form pallida. After the deposition of 

 the first three batches of ova, the same parent beetles were 

 placed in normal conditions, and two more batches were laid. 

 These, reared under natural conditions, gave normal decem- 

 lineata, which continued to breed true to type. The origin of 

 the pallida forms may therefore fairly be ascribed to the 

 abnormal conditions to which their parents were for a time 

 exposed. Two of these pallida males were mated with decem- 

 lineata females ; the resulting hybrids resembled normal 

 decemlineata. Now comes an interesting point. This genera- 

 tion of apparently normal decemlineata gave, when bred inter 

 se, offspring consisting of pallida, decemlineata, and decem- 

 li?ieata-\ike hybrids in Mendelian proportion. The pallida of 

 this generation bred true, being evidently extracted recessives ; 

 the decemlineata and hybrids broke up again in Mendelian 

 fashion. This most interesting experiment points to at least 

 three results of great biological importance. The first, which 

 is that in which we are more immediately interested, is the 

 confirmation of Weismann's view as to the accessibility of the 

 germ-plasm to external influences. The second is the demon- 

 stration that just as the somatic plasm has a period of highest 

 susceptibility, which fact was known to Weismann at the 

 time of his C. phlaeas experiments, so also the germ-plasm 

 itself has a similar period. This was not known to Weismann ; 

 if it had been, it might have led him to modify in some 

 respects his conclusions from those experiments. The third 

 point is the establishment of the fact that the type-form 

 of a given species may stand in Mendelian relation with a 

 variation of that species artificially induced by interference 



