18 Mr. J. W. Tutt on recent Experiments im 
eggs; (2) the differences in the general character and 
appearance of the imagines; (3) the difference in the 
shape of the wings, those of 7. crepuscularia being much 
the squarer; (4) the independent life-histories of the two 
insects; (5) the constant difference in the times of ap- 
pearance, even when inhabiting the same wood; (6) the 
fixed double-brooded habit of 7. bistortata, the fixed 
single-brooded habit of 7. crepuscularia; (7) the fact that 
the two insects breed true and always produce their own 
kind. On the other hand, those who maintain the specific 
identity of the species, do so on the ground that they are 
not able to refer with certainty occasional individual 
specimens to one or the other species. So far as the 
distinctness of two insects with perfectly independent and 
distinct life-cycles allows us to constitute them as separate 
species, these may be so considered. 
Both species are subject to melanic variation. Melanic 
aberrations of 7’. bistortata are exceedingly rare, and 
almost confined to South Wales; on the other hand, 
melanic specimens of 7. crepuscularia are very generally 
distributed in certain districts, such as Delamere Forest, 
Yorkshire, Mansfield (Notts), Derby, Swansea district 
(South Wales), &c. There is no district known where 
only the melanic form occurs, the typical form being 
regularly present in all localities in which it is taken. 
The melanic form of 7. crepuscularia is known as ab. 
delamerensis, B.-White. 
Dr. Ripina’s EXPERIMENTS. 
ORIGIN OF PARENTS USED FOR ParRINnGs.—BPy a little 
judicious artificial treatment during February and March, 
1897, Dr. Riding obtained a pretty free emergence of 7. 
bistortata, T. crepuscularia and T. ab. delamerensis. These 
insects were the parents of the hybrids and were obtained 
as follows :— 
(1) 7. bistortata.—These were (a) from eggs laid by a 
female of the second brood in July, 1896, and captured at 
Clevedon (Somerset), (b) eggs laid by female (second brood) 
bred by Mr. Bacot also from Clevedon ova. The imagines 
emerged between February 17th and March 27th, 1897. 
These were of the large, well-marked, ochreous, spring- 
form, known as ab. abietaria, Haw. 
