December 23, 1897] 



NA TURE 



,87 



noteworthy inasmuch as they differ considerably from the re- 

 sults of heating and cooling in other species. Their peculiar 

 relation to the temperature conditions is also remarkable ; thus, 

 summer pupae kept at 33° F. for ten weeks, if afterwards allowed 

 to remain at 55° F. , gave the cold form in its extreme develop- 

 ment ; but if forced at 90°, gave the heat form almost as per- 

 fectly as those kept at 80° to 90° all through. Another curious 

 point is that whereas a temperature of 47' F. was very injurious 

 to the pupae, they bore icing at 33° F. for ten weeks without 

 damage. 



Lencophthalmia punclaria, L., which was also tried during 

 this year, gave results in some respects like the above. Thus, 

 though forcing at 90° F. or icing at 33° were borne without 

 injury, exposure to 45° proved harmful. Again, as in C. phlceas, 

 "a temperature of 33° F. seemed to suspend the physiological 

 changes without much other effect," for the pupae exposed to 

 this temperature for over three months, and afterwards forced, 

 gave the heat form in almost as complete a state of development 

 as those forced from the beginning. Summer pupae were used 

 for the experiment, and the general effect of cooling was to 

 cause ' ' gradual disappearance of the submarginal blotches, in- 

 crease of dark sprinkling, and intensification of the central line 

 as the temperature was lowered." 



To Mr. Merrifield's account of his experiments during this 

 year a short paper was appended by the present writer, giving 

 reasons for considering certain of the modifications produced in 

 V. atalanta by both heat and cold to be ancestral in character.^ 

 Some of the new features produced by heat were considered to 

 show an approach towards V. callirrkoe, Hb. , and some of those 

 produced by cold appeared to indicate reversion to a still older 

 form of Vanessa. 



Experiments in 1893. — A number of winter pupje of Picris 

 napi, L., were divided into groups, some being forced in 

 February and March, others left to emerge out of doors, which 

 they did in late April and early May. The two divisions showed 

 the same kind of difference, though in less degree, as was 

 apparent in the summer brood of 1892 between those forced 

 throughout and those cooled for the greater portion of their 

 pupal period. 



Experiments on both summer and winter pupK of Pararge 

 egeria, L. , showed that the general effect of forcing was to lighten 

 the ground colour and cause the pale spots to become smaller and 

 less well defined. In no case was any approach shown to the 

 bright ochreous colouring of the South European form. 



In Hydriomena silaceata, Hb., cooling the summer pupae 

 caused an approach towards the usual colouring of the spring 

 emergence ; while forcing, besides producing a more uniform 

 appearance, generally diminished the size of the perfect insect. 



A trial was also made of the summer pupte of Araschnia 

 Icvana. The results were in general accordance with those 

 previously obtained by Weismann ; the effect of a raised tem- 

 perature being to produce the dark prorsa form, and that of low 

 temperatures (from 48° F. downwards) being to cause the 

 appearance of the pure levana type, a few of those only exposed 

 to moderately low temperatures showing slight traces of the 

 intermediate /^jrz'wa colouring. 



Interesting experiments were made on four species of Vanessa 

 — V. polychloros, L., V. atalanta, L., V. c-albuin, L. , and V. io, 

 L. Pupae of V. antiopa, L., gave negative results, probably in 

 consequence of being already too far advanced when their 

 treatment began. 



In V. polychloros, high temperatures caused a general lightening 

 of the ground colour and the appearance of yellowish clouds and 

 streaks ; the ordinary black spots were sharply defined. It was 

 found that yellowish marks made their appearance to a greater 

 or less extent when a temperature of 80 or upwards was em- 

 ployed, even if the pupa; had previously been cooled or iced for 

 some weeks. When exposed to low temperatures, the pupae 

 produced perfect insects with a deeper and duller ground colour 

 and a spreading of the dark marks, especially of the sub- 

 marginal band. The enlargement of this band was always 

 observed in cooled or iced specimens, whether subsequently 

 forced or not. The whole ground-area was generally dusted 

 with black scales, which tended to form new spots, especially in 

 a row parallel to the outer margin in both fore- and hind-wing 

 (Fig. 13)- . 



Fresh experiments on V. atalanta confirmed the previous 

 year's results and added new ones. Forcing temperatures up 



1 Weismann has expressed his general concurrence with these and sub^ 

 sequent conclusions of the present writer as to reversion (.V.f«< Versuchei 

 Jena, 1895, pp. 51, 72). 



to 100° F. were employed, with the result of killing many of the 

 pupae. Those specimens that emerged showed a scarlet cloudy 

 patch in that portion of the fore-wing which corresponds to the 

 centre of the ocellus in V. io ; and some of them showed another 

 new scarlet spot on the under side of the fore-wing, in addition 

 to the new spot observed in 1892. One of the apical white 

 spots tended to be loosely ringed with scarlet in the forced, and 

 with white in the cooled specimens. The latter were generally 

 undersized. 



In V. c-albtim it was found that both the first and second 

 brood, but especially the first, became darker if exposed to a 

 moderately low temperature. 



Forced specimens of V. io showed a tendency to the develop- 

 ment of dark spots near the apices of the nervular interspaces. 

 Cooled and iced specimens showed a tendency, increasing as the 

 temperature was lowered, for the dark costal "claw-mark" of 

 the fore-wing to lose its regular curve and become angulated, 

 for the apical pale spots to separate themselves more distinctly 

 from the remains of. the dark submarginal band, and for the 

 bluish constituents of the ocellus in the hind-wing to divide 

 themselves into two parallel series, a marginal and a sub-- 

 marginal. The resolution of the ocellus in the fore-wing was in 

 one specimen very complete (Fig. 11). 



A paper by the present writer drew attention to the further 

 reversionary features disclosed by the temperature modifications 



Fig. II. — Vanessa io. Fig. 12. — Vanessa Fig. 13. — 



(Diagrammatic.) Iced; polychloros. (Dia- Vanessa poly- 



showing resolution of grammatic.) chloros. (Dia- 



ocellus. Forced ; shows grammatic.) Iced 



size of black shows tendency 



marks somewhat to formation of 



reduced. The yel- new submarginal 



low markings are row of black 



not represented. spots (a) in fore- 



and hind-wing. 



above described, and commented on the significance of these 

 phenomena with reference to the centripetal and centrifugal 

 theories of heredity. 



Experiments in 1894. — Pupae of Limenitis sibylla, L., were 

 found to be intolerant of heat. Those that survived a tempera- 

 ture of 85° to 90° F. gave rise to perfect insects with a slight 

 increase of reddish scales near the apex of the fore-wings and 

 the anal angle of the hind-wings. The orange-brown of the 

 under surface was enlarged in area and paler in colouring. Ex- 

 posure to a temperature of 48° F. for from three to five weeks 

 caused a sprinkling of the white band with black scales, and on 

 the under surface an increase in area and intensity of some of 

 the darker parts with a tendency to suffusion and spreading of 

 the white. 



As a result of further experiments on Vanessa c-albttvi, it was 

 found that in certain of those exposed to low temperatures, 

 which were not well borne by this species, there was an increase 

 in the distinctness of the submarginal series of dark spots. Some 

 of these were pupilled with bluish or lavender scales, as in the 

 Chinese V. c-aureum, L., which appears to present an early 

 form of the Vanessa pattern. 



A few experiments were also made on V. cardui, L. , giving 

 results in accordance with those previously obtained by Stand- 

 fuss in Ziirich. 



Experiments in 1895. — Both high and low temperatures 

 (98° F. and 33° F. ) were found to be well borne by pupce of 

 Gonepteryx rhamni, L. Little change was produced in the 



NO. 1469, VOL. 57] 



