INCIDENTAL PHENOMENA RELATING TO METAMORPHOSIS IN LEPIDOPTERA. 35 



1889, one male ; March 22nd-April 4th, 1890, five females ; and April 

 16th, 1890, one male. Fenn notes an occasion on which E. versicolor 

 passed five years in the pupal stage. Satumia pavonia, in the Orkney 

 Isles, pupated in July, 1866, four imagines emerged between May 

 23rd-June 16th, 1867, all females, whilst three appeared in April, 

 1868, all males (Trail). Hellins states that more than half the pupae 

 of Eupithecia expallidata that one gets pass two years in the pupal 

 state. Fletcher notes the appearance of six moths of Endopisa nigri- 

 cana from a large batch (larvae collected end of July, 1872) on August 

 19th-22nd, although kept in a fireless room, most, however, emerged 

 during June and July, 1873, although one did not emerge until 

 June 1st, 1874, all being kept under the same conditions. From 

 Emmelesia unifasciata larvae collected in 1871, imagines emerged in 

 1872, 1873, and 1874 (Jones). Pupae of Centra vinula formed in 1862 

 produced imagines in June, 1864 (Horn). Cucullia scrophidariae 

 larvae collected 1894, several imagines emerged March, 1895, two or 

 three in 1896, none in 1897 or 1898, seven between April 29th- 

 May 8th, 1899, having been in the pupal stage five years (Tutt). 



There must be several elements that result in the causation of 

 the retarded emergence of the lepidopterous imago, or, perhaps, it 

 would be generally more correct to say, of the retarded development 

 of the lepidopterous imago. Some species, especially those that are 

 strictly northern, e.g., Petasia nubeculosa, appear normally to extend 

 the pupal stage, apparently without injury, over a period of three, four, 

 or five winters, and then to emerge satisfactorily. Other species 

 widely distributed over our Islands— Eupithecia venosata, E. togata, 

 Emmelesia albulata, Endromis versicolor, Satumia pavonia, &c., occa- 

 sionally pass a second winter as pupae even when derived from a 

 southern source, but do so frequently even when northern pupae are 

 brought south, in fact, such pupae are more prone to delay their 

 development when brought south, than when reared in their own 

 latitude under normal conditions. In such instances as these, the delay 

 appears to arise rather from an excess than a defect of temperature 

 and Chapman notes that " this appeared to be especially demonstrated " 

 when, some years ago, he attempted to force the pupae of several 

 species early in the winter. Not one of the pupae, he says, " would 

 be forced, they resisted the high temperature in the winter, throughout 

 the spring, when their proper season for emergence arrived, and went 

 over the next summer and winter. These pupae included some 

 JHanthoeciae, which are rather prone to taking a second winter, some 

 Geometrids, and some Ciicullia verbasci, which does not often take a 

 second winter. It is as though these pupae felt that the proper season 

 for emergence had arrived or past, before they had made a move, and 

 tbey must therefore wait till next season." There can be no doubt that 

 many pupae require a minimum time to more or less perfect certain 

 organs before the rapid histogenesis resulting in the final imaginal 

 development is possible, and that this final histogenesis is impossible 

 until a certain condition of the tissues (or of the histolytic products) 

 has been reached, and that this can only be reached under certain 

 external conditions of environment of which a high temperature may not 

 be one. Having reached this stage a gentle forcing, judiciously increased 

 after a time, generally produces successful results. Thus many 

 Sphingid pupae that will rarely respond to a forcing treatment when 



