542 IIEMIPTERA 



nectidae) they are entirely absent. The offensive matter emitted 

 by JVotonecta is of a different nature, and is probably anal in 

 origin. 



Metamorphosis or postembryonic development. — In the 

 language of the systematists of metamorphosis, Hemiptera are 

 said to be Homomorpha Paurometabola — that is, the young 

 differ but little from the adult. According to Brauer's general- 

 isations they are Menorhynchous, Oligonephrous, Pterygogenea, 

 i.e. they have a sucking mouth that does not change during life, 

 few Malpighian tubes, and are winged in the adult state. It is 

 generally admitted that the Homoptera do not completely agree 

 with Heteroptera in respect of the metamorphosis, it being 

 more marked in the former, and in Coccidae attaining (as we 

 shall mention when discussing that family) nearly if not quite 

 the condition of complete metamorphosis of a peculiar kind. 

 Unfortunately we are in almost complete ignorance as to the 

 details of the life-liistories and development of Heteroptera, so 

 that we can form no generalised opinion as to what the post- 

 embryonic development really is in them, but there are grounds 

 for supposing that considerable changes take place, and that 

 these are chiefly concentrated on the last ecdysis. The young of 

 some bugs bear but little resemblance to the adult ; the magnifi- 

 cently-coloured species of JEusthcncs (Fig. 255), before they attain 

 the adult condition are flat, colourless objects, almost as thin as a 

 playing-card ; it is well known that the extraordinary structures 

 that cover and conceal the body in Plataspides, Scutellerides, 

 Membracides, etc., are developed almost entirely at the last moult : 

 it is not so well known tliat some of these changes occur with much 

 rapidity. A very interesting account of the processes of colour- 

 change, as occurring in Pocciloccvpsus lineatns at the last ecdysis, 

 has been given hy Lintner,^ and from this it appears that the 

 characteristic coloration of the imago is entirely developed in 

 the course of about two hours, forming a parallel in this respect 

 with Odonata. When we come to deal with Aphidae we shall 

 describe the most complex examples of cycles of generations that 

 exist in the whole of the animal kingdom. 



Fossil Hemiptera. — Hemiptera are believed to have existed 

 in the Palaeozoic epoch, but the fossils are not numerous, and 

 opinions differ concerning them. Eugercun hochingi, a Per- 

 ' In Slingerland's Cornell Univ. Bull. No. 58, 1893, p. 222. 



