Care of the Young in the Animal Kingdom. 159 



mate, nevertheless sometimes lay eggs capable of 

 development. This phenomenon has been called by 

 Ch. v. Siebold, 1 to whom we are specially indebted 

 for its discovery, virgin-generation, or parthenogene- 

 sis. Under natural conditions parthenogenesis occurs 

 with ants principally in colonies which have lost their 

 queen, and therefore try to rear their posterity from 

 eggs laid by workers. In several observation-nests 

 of Polyergus rufescens, Formica sanguinea and rufi- 

 barbis the queen was missing, and I observed that the 

 workers, with Polyergus the slaves, selected an extra 

 large worker of the dominant species as a substitute 

 for the queen, treated her with greater care, gave her 

 more food, and thus induced her to parthenogenetic 

 oviposition. This shows that under certain circum- 

 stances the instinct of ants is able to effect by special 

 treatment the development of the ovaries of even 

 adult workers, so as to make them capable of laying 

 eggs ; 2 but these unfertilized eggs can only produce 



J ) "Wahre Parthenogenese bei Schmetterlingen und Bienen," 

 Leipzig, 1836. Quite recently Ch. Janet has discovered parthenogenesis 

 also among hornets (Sur Vespa Crabro, Extr. des Mem. de la Soc. 

 Zool. de France, 1895, p. 75). 



") This form of parthenogenesis, which is spontaneouly caused by 

 the workers themselves, must be carefully distinguished from another 

 form caused by artificially raising the temperature, and quite independent 

 of the ants' instinct. See my observations in "Biolog. Centralbl.," XI 

 (1891), No. 1: "Parthenogenesis bei Ameisen durch kuenstliche Tem- 

 peraturverhaeltnisse." The experiments made by E. Bickford ("Ueber 

 die Mbrphol. und Physiol. der Ovarien der Ameisen-Arbeiterinnen," 

 in "Zool. Jahrb. Abth. fuer Systemat," IX, 1895, 1st issue) with 

 Lasius fuliginosus (p. 19; Sep., p. 23) belong rather to the second 

 category than to the first, since she too employed artificially raised 

 temperature. At any rate, they do not approach natural conditions as 

 closely as my observations mentioned above. On the latter cf. "Stett. 

 Entom Ztg.," 1890, pp. 303-305, and "Biolog. Centralbl.," 1895, pp. 

 609 and 610. 



