442 THE POPULAR SCIENCE MONTHLY 



dreds of adults from a single original egg by a process not unlike that 

 employed in the egg-shaking experiments of our laboratories, this phe- 

 nomenon, though restricted to comparatively few species, is neverthe- 

 less of considerable economic importance. 14 



7. The development of social life among insects. This, as I have 

 shown on former occasions, has its origin both ontogenetically and 

 phylogenetically in the parasitism of the offspring on the parent. 15 



Paleontology seems to show very clearly the conditions that have 

 favored the enormous development of parasitism among insects espe- 

 cially within comparatively recent times. Some of these conditions 

 are: 



1. The diminution in insect stature which occurred in the late Car- 

 boniferous and during the Permian and seems to have been originally 

 in great part an adaptation to increased reproduction and dispersal. 

 Other things equal, a small animal will, for very obvious reasons, be- 

 come a parasite more easily than a large one. 



2. The development of metamorphosis. This was already clearly 

 established in the earliest known insects, the Paleodictyoptera, which 

 were predatory and amphibiotic like the may-flies of the present-day, 

 living in the water during their apterous larval stages and spending 

 their winged imaginal stage in the air. They show plainly the great 

 peculiarity of insect development, i. e., metamorphosis succeeding 

 growth and not preceding it as in the crustaceans, mollusks and anne- 



14 The occurrence of polyembryony was first clearly recognized and thor- 

 oughly investigated by Marchal in Eucyrtus fuscicollis ("Recherches sur la 

 Biologie et le developpement des Hymenopteres Parasites. I. La Polyembryonie 

 Specifique on Germinogonie, " Arch. Zool. Exper. Gen. (4), II., 1904, pp. 257- 

 335, 5 pis., and an earlier paper: "La dissociation de l'oeuf en un grand 

 nombre d'individus distincts chez l'Encyrtus fuscicollis," C. B. Acad. Sci. Paris, 

 CXXVI., 1898, pp.- 662-664), although Bugnion ("Eecherches sur le developpe- 

 ment postembryonnaire, l'anatomie et les moeurs de l'Encyrtus fuscicollis," 

 Bee. Zool. Suisse, V., 1891, pp. 435-534, 6 pis.) had previously studied the same 

 insect. Silvestri has published several valuable papers on polyembryony, the 

 most important being ' ' Contribuzioni alia Conscenza Biologica degli Imenotteri 

 Parassiti. I. Biologia del Litomastix truncatellus (Dalm.)," Ann. B. Scuola 

 Sup. d'Agric. Portici, VI., 1906, pp. 1-51, 5 pis. 



15 Wheeler, ' ' Ants, their Structure, Development and Behavior, ' ' Columbia 

 Univ. Press, 1910. Recently Holmgren (" Termitenstudien, I. Anatomische 

 Untersuchungen, " B. SvensTc. Vetensk. Eandl., XLIV., No. 3, 1909, 216 pp., 

 3 pis., 76 text-figs.) and Eseherich (" Termitenleben auf Ceylon," Gustav 

 Fischer, Jena, 1911, 262 pp., 3 pis., 68 text -figs.) have accumulated much 

 evidence to support the conclusion that the mutual attraction among the indi- 

 viduals and the development of the castes of the termite colony are due to the 

 habit of these insects of feeding on the fatty exudates of one another's bodies 

 and on that of their queens. This may also be true of ants and other colonial 

 insects. A very similar method of feeding on the surface secretions of their 

 host-ants is adopted by certain myrmecophiles (Oxysoma, Attaphila and Myrme- 

 cophila) and certain parasitic ants (Leptothorax emersoni). 



