396 NATURAL SCIENCE. June, 



Insecta, viz., Thysanura, Ephemeroptera, Odonata, Plecoptera, 

 Platyptera, Dermaptera, Orthoptera, Thysanoptera, Hemiptera, is 

 contrasted with the indirect (complete metamorphosis) development 

 of the remaining seven orders, viz., Coleoptera, Neuroptera, 

 Mecoptera, Trichoptera, Lepidoptera, Hymenoptera, and Diptera. 

 The development of the individual in the first nine orders does not 

 differ materially from that of animals in other branches of the animal 

 kingdom which also have direct development. The fact that the 

 larvas resemble the adults of the more primitive Thysanura is 

 parallelled by many similar cases in the animal kingdom. It is the 

 usual rule that the younger stages of more specialised forms resemble 

 the adults of the more primitive forms of the same stock, and this 

 principle, discovered by Von Baer and Louis Agassiz, is the founda- 

 tion of all systematic researches in phylogeny. Such resemblances 

 have been traced between batrachians and fishes, especially by 

 Huxley, among the fishes themselves by Agassiz, by Beecher among 

 corals, trilobites, and Brachiopoda, by Jackson in Pelecypoda and 

 Echinodermata, and by several authors, including one of the signers 

 of this article, among Cephalopoda. Mr. Miall compares the 

 batrachians with insects as a more nearly parallel type, but in this is 

 there not some confusion ? The comparison can only be made with 

 those forms of insects having direct development. The batrachian 

 has no quiescent stage, occurring subsequently to an active voracious 

 larval stage, which last has provided by overfeeding for the existence 

 and development of a pupa-like resting stage. In the insects and 

 batrachians he introduces the term " adult transformations " for the 

 later changes in which the pupa changes into the imago and the tad- 

 pole into the frog. Mr. Miall thinks, because the frog and the 

 winged form are new and comparatively late additions to the 

 primitive forms represented by the tadpole or the pupa, that 

 the incoming of these stages should be called " adult transformation " 

 or adult metamorphosis. 



The trouble that one has in adopting this term arises from the 

 general conception of the adult. This latter term is usually applied 

 to the sexually matured individual, and in " Bioplastology and the 

 Related Branches of Scientific Research " T one of the authors of this 

 paper has endeavoured to define this stage more or less, and also other 

 stages of the life of the individual. According to the nomenclature 

 there devised, and supposed to be natural, adult changes of structure 

 or characteristics, designated as sub-stages, are not confined to 

 insects, but occur in all animals, and are found equally in their old 

 age. The term " metamorphosis," however, in a technical sense, can 

 hardly be applied to these sub-stages. The life of the individual can 

 be divided and classified as follows, either in man or any of the 

 invertebrates, although in some animals whose existence is dependent 

 upon seasonal changes, e.g., Lepidoptera, it is questionable whether 

 1 Hyatt : Proc. Boston Soc. Nat. Hist., xxvi., pp. 59-125 ; 1893. 



