December 23, 1897] 



NA TURE 



185 



same general result was obtained as in the 1 888 experiments, 

 but the additional fact was established that "it was in the 

 pupal state that the effect was in the main produced. The 

 forced pupa;, whatever the treatment of the larvae had been, 

 invariably produced pale and comparatively spotless moths ; the 

 cooled or iced pupre, whatever the treatment of the larvK had 

 been, invariably produced dark and much spotted moths." It 

 was found that a temperature of 63° F., or even higher, was 

 low enough to produce the darker form. The treatment of the 

 larvie, though of slight effect compared with that of the pupae, 

 did not seem to be entirely without influence on the perfect 

 insect ; e.g the specimens that had been forced only as pupa; 

 were darker than those that had been forced all through. Some 

 individual variation was noticed in all the groups. Similar ex- 

 jjeriments on E. alniaria gave results tending in the same 

 direction, but less regular and striking. 



The effects on S. telralunaria were far more marked than in 

 1888. Pupae of the summer brood were iced for periods succes- 

 sively increased by two weeks up to twenty weeks. These 

 yielded moths becoming generally, but not regularly, more and 

 more like those of the spring emergence, both in colour and 

 pattern, as the period of icing was lengthened. The converse 

 experiment of forcing pupae of the autumn brood, which would 

 naturally give rise to the spring form of the perfect insect, 

 proved very injurious to the pupae, the majority of which died even 

 when the temperature was kept at 60° F. only. The moths that 

 emerged were irregular in their time of appearing, and poor in 

 condition. In colouring they were intermediate between the 

 summer and spring forms, those that remained longest in the 

 pupal stage being as a rule the darkest. This autumn spring 

 brood, like the corresponding brood in V. levana, is evidently 

 far more resistent in its colouring to temperature conditions than 

 the summer one. 



In all three species it was found that the period of pupation 

 was longer for males than for females : most so in E. alniaria, 

 least in S. tetralunaria. 



The broods of S. tetralunaria that had fallen off in 1888 

 showed still further deterioration, both as to health and size, in 

 the spring emergence of 1889. But some eggs of the degenerate 

 race that were sent to Wimbledon produced once more much 

 larger, more numerous and more healthy moths. The cause of 

 this was apparently the change of condition, and especially the 

 substitution of cherry for birch as the food plant. 



As a result of this year's experiments, Mr. Merrifield came 

 to the conclusion that the predisposition to assume one or other 

 form in a seasonally dimorphic species can in some cases be 

 completely controlled by external influences applied to egg or 

 larva before the end of its growth ; but not, except partially, 

 after larval growth is finished. 



Experiments in 1890. — In the course of 1890 the new fact 

 was established that different portions of the pupal period were 

 of different importance for the changes induced by temperature, 

 and that the pattern or outline of the markings could be made 

 to vary independently of the general colouring. It was proved 

 to be possible to obtain by difference of treatment, from the same 

 brood of a seasonally dimorphic species, individuals showing (i) 

 summer markings with summer colouring, (2) summer mark- 

 ings with an approach towards spring colouring, (3) spring 

 markings with summer colouring and (4) spring markings 

 with almost the spring colouring. 



A brood of spring larvae of the light-coloured strain of .S". 

 tetralunaria, which would naturally have produced moths of the 

 summer form, was forced as a whole ; pupating in June. Some 

 of the pupa; were kept at 80° F., these produced well-marked 

 summer forms (Fig, i). The rest were iced for about twelve 

 weeks, and then either forced or put out of doors. Those that 

 were forced after icing produced moths all of which had the 

 summer colouring, and most of which showed the spring mark- 

 ings (Fig. 3). Some of these which were cooled at 43° F. after 

 the colours of the wings had begun to appear under the forcing 

 process, showed no difference from the rest. Those that were 

 put out of doors after icing (temperature at 8 a.m. averaging 

 about 57° F. ) gave moths with the spring markings and a dark 

 colour in some cases almost reaching that of the spring emerg- 

 ence (Fig. 4). Similar experiments on two other broods gave 

 corresponding results, and showed that, in some instances, from 

 two to three days forcing during the last part of the pupal stage 

 might be enough to produce a very marked effect upon the 

 colouring. Another brood, of the third generation, which fed 

 up rapidly and pupated before the middle of August, gave rise 



NO. 1469, VOL. 57] 



at the ordinary temperature of the room (between 65° and 70" 

 F. ) to moths of the usual summer markings and colouring, but 

 slightly darker than their forced parents. When twelve of these 

 had emerged, the remaining pupae were cooled at about 43° F. 

 Those moths that einerged after twenty-six days cooling, while 

 still showing the summer markings, presented an approach to the 

 spring coloration (Fig. 2). 



Some striking results were also obtained with E. autuvmaria. 

 Forcing the pupa; produced, as in 1889, pale and comparatively 

 spotless moths (Fig. 5). When the pupae were cooled for four- 

 teen days or more before forcing, the ground colour became 



Fig. I. — Selenia tetralunaria. 

 Summer markings and colouring. 

 (Forced.) 



Fig. 2. — Selenia tetra- 

 lunaria. Summer mark- 

 ings, spring colouring. 

 (Cooled.) 



Fig. 3. — Selenia tetralunaria. Fig. 4. — Selenia tetralunaria. 



Spring markings, summer colour- Spring markings and colour- 



ing. (Iced, then forced.) ing. (Iced.) 



All the above were obtained from summer pupae. Figs, i, 3 and 4 are 

 from the same parents. The difference should be noted in the shape of 

 the inner area of the wings between Figs, i and 2 on the one hand, and 

 Figs. 3 and 4 on the other. 



dulled and the spotting blurred. Pupae cooled for seven to 

 twenty-eight days and then kept at the ordinary temperature of 

 the room gave rise to moths as a rule very much darker than 

 those finally forced ; darker even than moths from pupae that 

 had been cooled for five or six weeks before forcing. The 

 darkest moths of all were obtained from pupae cooled for five or 

 six weeks and then allowed to develop at the ordinary outdoor 

 temperature, or this followed by cooling (Fig. 6). Even in 

 these, forcing after eight days' exposure out of doors was found 

 sufficient to counteract largely the tendency to darkening. 



Fig. ^.—Ennomos autumn- FiG. 6.—Etinotnos autumnaria. 



aria. (Forced.) (Iced.) 



Both the above are from the same parents. 



Experiments with S. tetralunaria and E. autumnaria, on 

 the effect of moisture applied during the pupal stage in combina- 

 tion with various kinds of temperature, gave negative results. 



A few trials of the effects of temperature on Vanessa urtica, L. 

 and Lasiocampa quercus, L. , var. callume, were made this year, 

 with the general result that cooling the pupa caused enlarge- 

 ment of the blue and dark marks in V. urticiz ; while forcing 

 the pupa caused increased paleness in L. callunce, making it 

 approach in aspect the ordinary Z. quercus. 



The suggestion was thrown out by Mr. Merrifield that the 

 changes of pattern produced by temperature might assist in- 

 vestigators in tracing the evolution of the wing-markings in 

 modern forms. 



