INSECT PARASITISM 441 



hence from the need of an active and inquisitive first larval stage to 

 supply this defect. 



2. The prevalence of hyperparasitism. "We may distinguish pri- 

 mary, secondary, tertiary, quaternary and even quinary parasites among 

 insects, according to the principle of the "little fleas ad infinitum." 

 The numerical appellations in this series have been restricted to in- 

 sects parasitic on other insects, although the primary parasites are 

 really secondaries when they attack insects like caterpillars, since these 

 are, of course, plant-parasites. 10 



3. The absence in parasitic insects of hermaphroditism, a phenome- 

 non so prevalent among vermian, crustacean and annelidan parasites. 

 Only one small group of insects is known to be hermaphroditic, namely, 

 the Termitoxeniidae, comprising a few genera of extraordinary flies that 

 live in termite nests. 11 



4. The rare occurrence of heteroccism, or change of host, a phenom- 

 enon very prevalent among tapeworms and flukes. It has been de- 

 veloped, however, within apparently very recent times in such groups 

 as the plant-lice and in certain myrmecophilous beetles of the genera 

 Atemeles in Eurasia and Xenodusa in North America. 



5. The increasing development of viviparity as seen in such a series 

 of parasites as Hemimerus, which, according to Hansen and HeymonSj 

 develops within the ovary of its mother, 12 the larviparous Tachinidas 

 and Sarcophagidas, the nymphiparous Hippoboseidae, ISTycteribidae and 

 plant-lice, and the Termitoxeniidaa which, according to Wasmann, are 

 born practically as adult insects. 13 



6. The development of polyembryony among the Chalcidid and 



Proctotrypid Hymenoptera. Owing to the greatly increased reproduc- 



tivity of these parasites through the formation of dozens or even hun- 



10 Fiske ("Superparasitism: An Important Factor in the Natural Control 

 of Insects," Joum. Econ. Ent., III., 1910, pp. 88-97) and Pierce ("On Some 

 Phases of Parasitism Displayed by Insect Enemies of Weevils," ibid., III., 

 1910, pp. 451-458) have distinguished between "hyperparasitism" and "super- 

 parasitism. ' ' The former term is denned by Pierce as ' ' the normal attack of a 

 parasite species upon another parasite species, ' ' whereas superparasitism ' ' occurs 

 when a normally primary parasite attacks a host already parasitized, and the 

 result is that the latest comer generally attacks its predecessor. ' ' The distinc- 

 tion is important, but for the sake of brevity I have not introduced into the 

 text. 



11 Wasmann, ' ' Termitoxenia, ein neues fiugelloses, physogastres Dipteren- 

 genus aus Termitennestern, " 2 Pts., Zeitschr. f. wiss. Zool., LXVIL, 4, 1900, 

 pp. 559-617, LXX., 2, 1901, pp. 289-298, and Assmuth, "Termitoxenia Ass- 

 muthi Wasm. ; Anatomisch-histologische TJntersuchung, " Inaug. Dissert., 1910, 

 53 pp. 



12 Cf. Hansen, ' ' On the Structure and Habits of Hemimerus talpoides 

 Walk.," Entom. Tijdskr. Arg., XV., 1894, and Heymons, "Eine Plazenta bei 

 einem Insekt {Hemimerus)," Verh. deutsch. zool. Gesellsch., 1909, pp. 97-107, 

 3 figs. 



13 Zoo. citato. 



