ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 208 



requires him to visit certain flowers lie comes to them witli certainty, if 

 his sense of smell is well developed, or by chance, if it is not. Incapable 

 of distinguishing different flowers by their forms, he hastens towards 

 coloured spots, hesitates, and only decides when he is close enough to 

 know by their odour whether he has found what he was seeking. The 

 same is true of living prey ; if it is ordinarily immobile it is known by 

 its odour, if it is agile it is recognized by its movements. Smell or 

 smell with sight bring about the congress of the sexes. The perception 

 of movements warns the insect of the approach of an enemy. Prof. 

 Plateau feels that in thus insisting on the imperfect visual power of 

 Insects he is taking up a position which is opposed to deeply seated 

 beliefs, but he bases himself on his experiments, and demands that he be 

 answered by experiments alone. 



a. Insecta. 



Anatomy and Biology of Physapoda.* — Dr. K. Jordan gives an 

 account of the group of Insects to which the term Thysanoptera is often 

 applied, and which Prof. Glaus — for examj)le — more correctly calls 

 Physopoda. The author would separate these insects from the Ortho- 

 ptera, and establish a special order for them. He is of opinion that 

 the difference between Insecta metabola and ametabola is only apparent ; 

 the mode of development of the latter is not opposed to that of the 

 former; in the one case there is continuous, in the other interrupted 

 change, and between the two extreme types there are intermediate stages. 

 It is not true that all Orthoptera or Ehynchota are now ametabolous. 

 The Orthoptera amphibiotica have larvae which are unlike their imagines, 

 and may be called hemimetabola. Change goes still further in the 

 Coccidse among the Ehynchota, and the metamorphosis of the Physopoda 

 is quite similar to that of the Coccid^e. 



The palaeozoic insects are allied to Orthoptera, Thysanura, Homoptera 

 or Neuroptera, and the other orders of Insects only appear in mesozoic 

 or cainozoic periods ; palfeontology tells us nothing as to the point of 

 origin of recent insects. The Hemiptera appear to be derived from the 

 Homoptera, while all the rest are further developments of orthopteroid 

 or neuropteroid forms. The carboniferous Homoptera and Neuroptera 

 were probably derived from orthopteroid forms. And there appear, 

 therefore, to have been two series of developments arising from the 

 broad base of the Orthoptera — one to the Insecta holometabola, the other 

 through the Homoptera to the Heteroptera. The latter group have the 

 germinal stripes internal, and includes those insects whose larval stages 

 are anatomically similar to the imaginal ; among these the Physopoda 

 must be placed. 



When we come to inquire more closely as to their position we must 

 consider their special anatomy and biology. They, especially in their 

 larval state, resemble the small Cicadellinae ; the hypognathism of the 

 vesicular feet is so strongly marked that the oral cone comes to lie under 

 the prothorax ; the number and position of the ocelli calls to mind the 

 Orthoptera rather than the Hemiptera, while the position of the 

 antennaj is as much orthopteroid as aphidoid. In the development of 

 the mandibular organs the Physopoda do not differ as much as do the 

 Ehynchota ; the physopod proboscis is intermediate in type between 



* Zeitschr. f. WL-s. Zool., xlvii. (1888) pp. 541-620 (3 pis.). 



p 2 



