168 HINTS ON THE ANCESTRY OF INSECTS. 



organs of the Cecidomyian larva of Miastor, which produces a 

 summer brood of young, alive, and living free in the body 

 of the child-parent ; and in the pupa of Chironomus, which has 

 been recently shown by Von Grimm, a fellow countryman of 

 Ganin, to produce young in the spring, while the adult fly lays 

 eggs in the autumn in the usual manner. This is in fact a true 

 virgin reproduction, and directly comparable to the alternation 

 of generations observed in the jelly fishes, in Salpa, and certain 

 intestinal worms. We can now, in the light of the researches 

 of Siebold, Leuckart, Ganin and others, trace more closely than 

 ever the connection between simple growth and metamorphosis, 

 and metamorphosis and parthenogenesis, and perceive that they 

 are but the terms of a single series. By the acceleration in the 

 development of a single set of organs (the reproductive), no 

 more wonderful than the acceleration and retardation of the 

 other systems of organs, so clearly pointed out in the embryos 

 of Platygaster and its allies, we see how parthenogenesis under 

 certain conditions may result. The barren Platygaster larva, the 

 fertile Cecidomyia larva, the fertile Aphis larva, the fertile Chir- 

 onomus pupa, the fertile hydroid polype, and the fertile adult 

 queen bee are simply animals in different degrees of organiza- 

 tion, and with reproductive systems differing not in quality? but 

 in the greater or less rapidity of their development as compared 

 with the rest of the body. 



Another interesting point is, that while the larvae vary so 

 remarkably in form, the adult ichneumon flies are remarkably 

 similar to one another. Do the differences in their larval 

 history seem to point back to certain still more divergent 

 ancestral forms? 



These remarkable hyper-metamorphoses remind us of the 

 metamorphosis of the embryo of Echinoderms into the Pluteus- 

 and Bipinnaria-forms of the starfish, sea urchins and Holothuri- 

 ans ;* of the Actinotrocha-form larva of the Sipunculoid worms ; 



*It is a suggestive fact that these deciduous forms give way through histolysis 

 to true larval forms, just as in some flies (Musca vomitoria) the true larval lorm 

 goes under, and the adult form is built up from the hnaginal diskg of the larva. In 

 an analogous manner the deciduous, pluteus-condition of the young Echinoderm 

 perishes and is absorbed by the growing body of the permanent adult stage. This 

 deciduous stage of the ichneumon may accordingly be termed the prelarval stage. 

 Now as we find, insects with and without this prelarval stage, and in the radiates 

 quite different degrees of metamorphoses, the inquiry arises how far these differ- 

 ences are correlated with, and consequently dependent upon, the physical sur- 



