60 



the subiinaginal instar of the Ephemeridae, after moulting at the 

 surface of the water, tlies about for a few moments, then to moult 

 again and immediately afterwards to proceed to copulation, rather 

 be taken as a speciality of the Agnathous life history, without any 

 deeper signiticance, and therefore of no importance for the explana- 

 tion of Holbmetaboly with its dormant pupal stage. 



On this point I dare not pronounce a definite opinion, but should 

 like to point out, that in trying to find an answer to the above 

 stated question, we must take into account various general consi- 

 derations, in the first place that of the development of wings in 

 its totality, viz. the <piestiou how Insects (at least Pterygogenea) 

 acquired their wings. For this decides about the question whether 

 we are to suppose that the ancestors of modern Pterygote Insects 

 never passed through a period, in which they moved about on the 

 wing before attaining sexual maturity, or that the beginning of the 

 functional activity of the wings (howsoever acquired) became more 

 and more postponed to the last instar. If we are right in accepting 

 the second altei'uative, and therefore in believing that the oldest 

 winged insects could already make use of their wings shortly after 

 their birth, the Agnatha may have retained a last trace of this 

 ancient condition. The apparently absurd fact, that these animals 

 tly about in their subimaginal coat for a few moments only, might 

 then be explained by the assumption, that they graduallj' postponed 

 the start on the wing to later instars, under the ever increasing 

 influence of their secondary adaptation to life in the water. Then 

 the ditference between them and other Hemimetabola would not 

 consist in a greater originality of the latter, but in a different 

 mode of deviation from the primitive condition, viz. by the 

 complete removal of the initiation of real flying to the imaginal 

 instar. 



The supposition of such a retardation in the transition to flying 

 life-habits is diametrically opposed to the explanation assumed for 

 many other phenomena in metamorphosis, viz. that the manifesta- 

 tion of new characteristics is gradually removed to ever younger 

 instars. In my opinion the former supposition is as well justified as 

 the latter. When for instance Weismann (rightly I think) assumes 

 that changes in colour-mai'kings of certain caterpillars, becoming- 

 visible at their last ecdysis only, have been transferred to 

 younger stages in species near akin b}^ a process of precession 

 of development, the opposite course of events may also be consi- 

 dered possible, viz. that a colour-pattern of the wings, which origi- 

 nally came into existence together with the Avings themselves, now 



