312 THE entomologist's record. 



time tlie tissues have reached a certain stage of development, that some 

 change goes on inside the pujia, and that the imaginal structures 

 (digestive, respiratory, nervous, scale &c.) are perfected or formed in 

 the pupal stage, but from the statements made during the discussion 

 before referred to, it would appear that here most of us stop. 



As Professor Weismann's theory, that the tissues of the pupa 

 undergo " histolysis," appeared to be unknown to many of those 

 present it may be worth while to call attention to it. It was formerl}^ 

 supposed that, when the larva changed to a jiupa, the tissues simply 

 underwent a progressive development resulting in the formation of the 

 scales, &c., in other words that the imago Avas from the first in the 

 pupa with its parts, &c. formed, and that it simjily progressed in 

 development until maturity Avas reached. But Professor Weismann 

 has shown us by his exjDcriments that development in the pupal 

 period is in no way so simple as this idea would suggest, but that the 

 tissues of the larva, having reached a comj^aratively high degree of 

 perfection at the time of pupation, break down in the pupa and are 

 reduced to more elementary units, degeneration as it were setting in. 

 After this has been brought about, a raj^id regeneration takes place ; 

 new tissue is rapidl}' formed, new structures are built up, and the pupa, 

 instead of being, as we have been apt to consider it, in a particularly 

 inactive condition so far as really active changes in the tissues are 

 concerned, is probably more completely vitalised than is the egg or 

 larva, and is, therefore, very susceptible to any external influences 

 which might affect its vitalitj'. It is during this period that the wing- 

 membrane and scales are formed, together with the strictly pupal 

 structures. 



The knowledge of these facts has led man}' of our leading 

 lepidopterists to refer to the pupal structures rather as definite organs 

 of the pupa than as imaginal organs enclosed in cases. Thus we talk 

 of the wings or antennae which are seen in an empty pupa case (and 

 of course also in a living pupa) as the "wing-cases" or "antenna- 

 cases," whilst the same wing-cases with their contents are termed 

 " pupal- wings," and the antenna-cases with their contents " puj^al 

 antenna?," until the final stage of development. When development is 

 actually complete and the colour of the future imago becomes 

 conspicuous through the pujja case, the mature organs are frequently 

 termed imaginal wings, &c., although still confined in their pupal cases. 

 It is well, however, that we should remember that there are j^upal 

 organs and that differentiation of tissue and actual growth take place 

 in the stage. 



If we apply the simplest elementary laws relating to vital force to 

 the pupa, we shall find that the following facts hold good : — (1) The 

 pupa when first formed has a certain amount of inherent vital force by 

 means of which both the processes of " histolysis " and of " rehabili- 

 tation " are carried on in it. (2) That jDupa which has the nearest 

 approach to the normal amount of ^ntal force will undergo the most 

 perfect " histolysis " and " rehabilitation," and will produce an imago 

 most nearl}^ conforming to what is known as the normal tyj^e, that is 

 the type produced under the most healthy and satisfactory conditions. 

 Conversely that pupa whose amount of vital force is farthest removed 

 from the normal (whether in excess or in defect) is one in which 

 " histolysis " and " rehabilitation " will be least perfect, and the imago 



