in some stages of Thysanoptera and in the last instars of male Cocco idea and 

 Aleyrodidae in the last mentioned case already together with the internal po- 

 sition of imaginai discs. To a lesser extent every ecdysis is preceded by a trans- 

 itory immobility period together with the tзфical position of pupa, i. e. T^dth 

 the hung down head and legs closely tied to the body. On the other hand 

 in the phylogenetically lowest holometabola the immobility period of pupae 

 is considerably limited (e. g. in the family Sialidae and Raphidiidae) the pupae 

 being freely mobile through the greater part of their existence using their 

 organs and some of them (Raphidia) even accepting food. The state of con- 

 stant pupal immobihty is a precondition necessary for the development of 

 numerous further adaptations known by the present pupae, such as spinning 

 of cocoon, attaching of extremities to the body (pupa obtecta), formation 

 of puparium etc. On the other hand the occurance of inmobility anables the 

 coceon spinning also in other developmental stages, as in eonymphs of some 

 tenthrenidids. 



4. The pupa corresponds morphologically to the nymph of heterometabola 

 (in some languages, as in French both forms have the same name), physiological- 

 ly, however, only to the second half of the last larval instar of heterometabola. 

 Owing to the supplementary pupal moulting (cf. Hinton 1948) the meta- 

 morphosis period of heterometabola is divided into two instars, i. e. the last 

 larval instar and pupal instar, whereas the larval stage in different species 

 consists of a different number of instars, from the first to the penultimate one. 

 As phjdogenetically secondary must be considered also the division of meta- 

 morphosis into extern taking place in the last larval instar and intern one 

 in the pupal instar. 



Most of these hypotheses are well based upon the more ancient morphologi- 

 cal discoveries and in spite of controversial opinions of the above-mentioned 

 authors they are supported by the most recent investigations on metamorphosis 

 hormones (see Novak Ic). There is no space for the detailed analysis of the 

 whole question but still we wish to point out briefly several new discoveries 

 speaking unanimously for this conception. 



First of all, the non-existence of a direct correlation between the moulting 

 hormone, or ekdyson, (previously incorrectly called "growth and differenti- 

 ation hormone") and the morphogenesis was fully experimentally confirmed 

 in the work of Karlson (1957), Karlson and Lüscher (1958), Joly and 

 H alb Av ach s (1957). Similarly inconsistent are the arguments of e. g. Snod- 

 grass (1954) claiming that the number of moults is a sufficient reason against 

 the homology between pupa and nymph. If луе are able to induce or inhibit 

 the moulting by a simple implantation or extirpation of the source of moult- 

 ing or activation hormone and if this moulting can procède without any mor- 

 phological alterations, even without growth, then the fact alone of a change 

 in number of moultings cannot be ascribed a greater phylogenetical signifi- 



G6 



