l6o METAMORPHOSIS 



There are certain minute Hymenoptera that deposit their 

 eggs inside the eggs of other Insects, where the beings hatched 

 from the parasitic eggs subsequently undergo their development 

 and growth, finding their sustenance in the yolk or embryo con- 

 tained in the host-egg. It is evident that such a life is very 

 anomalous as regards both food and the conditions for respira- 

 tion, and we consequently find that these tiny egg-parasites go 

 throuojh a series of changes of form of a most remarkable 

 character.^ It would appear that in these cases the embryonic 

 and post-embryonic developments are not separated in the same 

 way as they are in other Insects. We are not aware that any 

 term has yet been proposed for this very curious kind of Insect 

 development, which, as pointed out by Brauer,^ is doubtless of a 

 different nature from the hypermetamorphosis of Sitaris. 



Changes in Internal Organs. 



In relation to the post-embryonic development of the internal 

 organs of the body there is but little exact generalisation to be 

 made, the anatomical condition of these organs at the time of 

 emergence from the egg having been ascertained in but few 

 Insects. We know that in Holometabolous Insects the internal 

 anatomy differs profoundly in the larval and imaginal instars. 

 As to Insects with more imperfect metamorphosis very little 

 information exists, but it appears probable that in many no ex- 

 tensive distinctions exist between the newly-hatched and the 

 adult forms, except in the condition of the reproductive organs. 

 Differences of minor importance doubtless exist, but there is 

 almost no information as to their extent, or as to the periods at 

 which the changes occur ; so that we do not know to what 

 extent they may be concentrated at the final ecdysis. In Insects 

 with perfect metamorphosis the structures of the internal organs 

 are, as we have said, in many cases totally different 'in the larval 

 and imaginal periods of the life ; but these changes are far from 

 being uniform in all Holometabola. The nervous system in 

 some cases undergoes a great concentration of the ganglia, in 

 others does not, and important distinctions exist in this respect 

 even within the limits of a single Order, such as the Coleoptera. 



^ See Prodotrupidae subsequently. 

 2 Verh. Zool.-boL Ges. JVien, xix. 1869, p. 839. 



