190 B. T. LOWNE ON THE HYMENOPTERA. 



development to certain forms of Crustacea is a point of the greatest 

 interest, and I look forward to some future researches yet to be 

 made to throw much light upon the origin of insects. 



Curious as the life history of Platygaster is, a yet more 

 marvellous one has to be told. Some years ago Sir John Lubbock 

 found a remarkable little hymenopterous insect, which used its 

 wings for the purpose of swimming under water, belonging to the 

 genus Polynema. The eggs of Polynema are very much like 

 those of Platygaster; but they are laidn(»t in the larva of another 

 insect, but in the egg. The adult Polynema seeks for suitable 

 eggs and deposits her own with them. The eggs thus chosen are 

 those of the beautiful green dragon fly, Agrion Virgo, which lays 

 its eggs in the buds of the water-lily. A group of cells united 

 together into a solid mass escapes from the egg of Polynema, 

 which hatches, in fact, as a protoplasmic yolk, which appropriates 

 the food yolk of the egg of another creature. At an early period 

 the egg of the dragon fly ceases in its development, but that of 

 the Polynema goes on until a larva is produced, which resembles 

 in appearance one of j the lower Annelids ; this too undergoes 

 changes similar to- those observed in the case of Platygaster, 

 and ultimately forms a larva just like an ordinary hymenopterous 

 larva, except that it never forms any tracheae, and remains entirely 

 without any such organs during the whole of its life. The Dragon- 

 fly's egg shell becomes now only a kind of case in which the de- 

 velopment of Polynema goes on. After a few days the egg shell 

 is broken, but instead of a larval Dragon fly, there emerges an 

 adult Polynema, which dives at once into the water. The wings 

 may be fairly believed to subserve the respiratory function in 

 - these insects, as they remain open sacs, the interior of which is 

 continuous with the body cavity of the insects. It is interesting 

 to remember that Oken believed the wings of insects to be modifi- 

 cations of respiratory organs, and homologous with the main tracheal 

 trunks. I do not know if, at this late period of the evening, I 

 should be justified in entering into the details of the history of the 

 other form of genus Ophioneurus, which I alluded to at the outset 

 of this paper. There are some differences between its develop- 

 ment and that of Platygaster and Polynema. I will only mention 

 the more important of these. Ophioneurus is aerial irstead of 

 aquatic; it is parasitic in the eggs of the common cabbage butter- 

 fly, and is, therefore, probably an easy form to obtain. Instead of 



