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THE AMERICAN NATURALIST [VoL.LV 



The egg is nearly always laid upon the body of the host 

 or thrust into it, usually the latter, to which purpose the 

 extrusible, stiletto-like ovipositor of the female is adapted 

 with great nicety. Oviposition may take place either in 

 the egg of the host, in the larva, or even in a later stage, 

 and the parasite may complete its development either in 

 the stage of the host in which it is laid, or development 

 may be delayed and not completed till the host has pro- 

 ceeded to a further stage in its ontogeny. Under such 

 conditions the larva is to a great extent passive, although 

 in its earlier minute stages it frequently exhibits {e.g., 

 in certain Serphoidea) great modifications in body form, 

 and develops monstrously specialized jaws or other or- 

 gans to aid in attacking the massive tissues or yolk- 

 masses of its host. 



When such modifications of the young larva are tran- 

 sitory and disappear almost completely after one or two 

 ecdyses, they form a transition to several very clearly 

 defined cases of hypermetamorphosis which have been 

 noticed in certain Chalcidoidea by several observers 

 (Wheeler, '07; Smith, '12, and Brues, '19). In members 

 of two families, the Eucharidae and Perilampidae, they 

 have found an active, free-living, first stage larva known 

 as a planidium which is quite similar to the triungulin 

 of the Meloid beetles and the Strepsiptera. Like them, 

 the planidium becomes helpless once it has become para- 

 sitic. Great interest attaches to the planidium, but until 

 its distribution is much better known it can not be con- 

 sidered of taxonomic value, especially as quite similar 

 larvre are known in several other orders of insects. 

 Another series of Hymenoptera, certain parasitic bees, 

 are known through the researches of Graenicher ('05) 

 and others to possess much larger jaws in the first larval 

 stage. As we have mentioned previously, the type of 

 parasitism in this case is very different, for the parasite 

 simply eats the host larva that it may appropriate its 

 food-supply, and we have a parallelism in structure, of 



