40 BRITISH LEPIDOPTERA. 



binds the silk and hardens the cocoon by a distinctly alkaline fluid 

 coming from the head. The southern races appear to spin, as 

 a rule, lighter (i.e., more yellow) cocoons than the northern forms, 

 but this is possibly due, in part, at least, to the drier conditions 

 under which they are spun, much variation often occurring, and 

 damp distinctly tending to produce darker coloured puparia, although 

 one suspects that the food must also considerably influence the 

 result, the darkening of the cocoon being largely dependent on the 

 final excretions of the larva, which we know are used to harden 

 the silk. Latter states (Trans. Ent. Soc. London, 1895,- pp. 407 — 

 8) that the cocoons of Lasiocampa qiiercus var. callunae, Lachneis 

 lanestris and Cochlidion limacodes, have many points in common, and 

 that all these have similar appliances for escaping. The cocoons are 

 all tough, more or less cylindrical with rounded ends, one of which is 

 raised as a lid at the time of emergence. The boring organ is of 

 a totally different kind from that existing in the Dicranurids, and 

 is not formed either by labial prongs or modified maxillary palpi, 

 nor does the anterior portion of the pupa form a " shield " to the 

 head and eyes of the imago. On the contrary, by carefully denud- 

 ing the head by brushing and blowing, it may be seen that the 

 head is far more turned down, so as to bring the mouth-parts into 

 a more backward position, while the median frontal portion of the 

 head between the eyes is produced forward into a prominent and 

 sharply-pointed umbo or boss (loc. cit., pi. ix., fig. 9/;) of great 

 strength, and capable of being used as a powerful awl in opening 

 the lid of the cocoon. There are slight differences in the details 

 observable in the three species named. L. var. callunae and Z. 

 lanestris have the boss developed to a less degree and less sharply 

 pointed on the head of the pupa also (loc. cit., pi. viii., fig. 8), while 

 in C. limacodes the converse holds good, the boss being far sharper 

 and stronger in the pupa than in the imago (loc. cit., figs. 10 — 12); 

 indeed, the pupal boss is the only hard structure in the otherwise 

 fragile and delicate pupa -case of this species, <x:c. Criticising this 

 statement, Chapman says {Ent. Rec, xiii., p. 299) that L. que re us 

 var. callunae, he believes, " breaks off a lid as do Cochlidion 

 limacodes and Lachneis lanestris, but more often it fractures very 

 irregularly, and often into several pieces; but it is a fracture rather 

 than caused by a solution, although Latter says that the imago 

 produces much alkaline liquid. In all three cases the force produc- 

 ing the fracture is the pressure, which the inflation of the imago 

 enables it to exert from ' within from end to end of the cocoon.' 

 The ' sharply - pointed umbo' merely determines the starting-point 

 of the fracture, i.e., it increases the strain immensely at one par- 

 ticular point, and as soon as fracture commences there it at once 

 runs round the whole lid. Mr. Latter is quite right in supposing 

 that the lid of C. limacodes is ruptured by the pupa, i.e., by the 

 imago within the pupa - skin, since, like all Incomplete, the un- 

 ruptured pupa emerges from the cocoon. The sharp point of the 

 pupa does not act, as Mr. Latter expresses it, 'as an awl,' but 

 makes the pressure the whole pupa is exerting a little more strenu- 

 ous at one point, tending to an angular bending o\ the cocoon at 

 that point, and so beginning the fracture. When a 'pupa incom- 

 pleta' lias to force its way through meshes of silk, as in most 



