94 



THE YOUNG NATURALIST. 



[May, 



stigma again, thus enclosing a marginal cell. In- other genera, this 

 branch is continued to near the apex, there becoming obsolete, and 

 sending off the return nerve to the stigma. This sudden stoppage of 

 a nervure is a very common phenomena in all insects, but is often 

 more apparent than real, and generally causes, when actually present, 

 an incomplete closure of a cell, the abrupt termination or " blind 

 lead " being most marked. Without the aid of a careful microscopical 

 investigation, however, it is impossible to accurately determine 

 whether a cell is really imperfectly closed, or only seemingly so, and 

 it is necessary to clearly distinguish between the two. Both instances 

 occur in the genus Ophion. The first sub-marginal cell in the anterior 

 wing is thus incompletely isolated, and the second discoidal cell appears 

 likewise incomplete until more minutely examined. By treating the 

 entire appendage with oil of cloves in the manner before stated, it 

 will then be found that the structure of the nervure undergoes a 

 natural, but sudden transition, thin, highly transparent, colourless 

 walls, being substituted for the thick, coloured membrane forming the 

 remainder of the ray. And were it not for the fact that the trachea 

 suffers no interruption, but as a black, convoluted thread, pursues the 

 even tenor of its way, it would be a matter of considerable difficulty 

 to prove the presence of the nervure at all. 



Some Hymenopterous genera are remarkable for the almost entire 

 absence of wing rays, but the location and course of the missing ner- 

 vures is generally marked by a brownish discolouration and thickening 

 of the membrane. Obsolete nervures may thus be traced in the 

 anterior and posterior wings of bees, and those of the Chalcidida are 

 more than commonly deficient in this respect. 



But the chief and best known characteristic of the wings of 

 Hymenoptera, is the arrangement for connecting, during flight, the 

 anterior and posterior wings in one unbroken plane. The under pair 

 are provided with a number of hooks, placed in a more or less irregu- 

 lar row, and having their bases immovably fixed to the costal nervure. 

 These curious appendages vary considerably in position and number, 

 some species possessing no more than two, while others are more 

 abundantly furnished with twenty and upwards. They are likewise 

 scattered all along the costa, and it is not unfrequent to find a double 

 set, as in Ophion, one section being placed near the base, and the 

 other about half distance from root to tip. They are very highly de- 

 veloped in the Apida, reaching an advanced degree of perfection, both 

 as regards solidity of structure and beautiful regularity of arrangement. 

 I have, in Fig. 3, given a magnified representation of the hooks as 



