36 M. Oscar von Grimm on the Agamic Ueproduction 



It is therefore an insect living principally in the water, per- 

 haps living only for a day or two, or even a few hours, in 

 another sphere. 



But if we remove from the perfectly developed insect, before 

 it has yet quitted the pupa-case, the ova which Avould other- 

 wise liave been subjected to fecundation, and preserve them 

 in water, the development of the larva takes place in them 

 also ; it only lasts a little longer (about six days), and is £i"e- 

 quently obstructed. 



We have thus seen that our CMronomus is subject to an 

 alternation of generations, namely to pfedogenesis. But this 

 case of psedogenesis is somewhat different from that of the 

 Cecidomyice^ in which the second generation is produced 

 agamically iDy the larva, and not by the pupa. This, how- 

 ever, of course, is of no very great consequence. Von Baer 

 has already expressed the opinion that different animals may 

 be subject to psedogenesis at different stages of development*. 

 But, at any rate, our case of pedogenesis unites that of the 

 CecidomyicB with the parthenogenesis of the Coccidte, for ex- 

 ample, especially because in the Chironomus the imago, which 

 requires impregnation, is developed chiefly (perhaps, indeed, ex- 

 clusively f) in the autumn — just as the Coccidaj produce their 

 ephippial ova after copulation, and the agamic eggs without 

 the cooperation of the male ; but the larvaj of the Ceci- 

 domyice become converted into the imago, according to 

 Wagner J, when they find themselves under favourable con- 

 ditions, without being subjected to the influence of the seasons. 

 We shall see hereafter that both the stmcture and the deve- 

 lopment of the ova of Chirotwnms demonsti'ate this transition, 

 inasmuch as they are perfectly identical with those of the 

 A})liides and otlier insects, but not with those of the Cecido- 

 myid larva?. 



Besides being subject to psedogenesis, our Chironomus ap- 

 pears to be not quite a stranger to parthenogenesis, at least in 

 some instances, perhaps induced by artificial causes. Par- 

 thenogenesis, as is well known, is the designation of the 

 agamic reproduction of perfectly developed but unfecundated 

 females, to which worker bees §, humble bees, wasps, Psy- 



* " Ueber Prof. N. Wagner's Entdockung &c.," M^l. Biol. del'Acad. 

 de St.-PtHersb. v. p. 280. 



t Tho instances of the development of tlie imago in spring have per- 

 haps been intiuenced by the temperatiu'e of the room and other ailifacial 

 causes. 



\ " Beitrag zur Lehre von der Fortpflanzung der Insectenlarveu," 

 Zeitschr. fiir wiss. Zool. ISO.?, xiii. p. 'y24. 



§ In tlie bees it occurs rarely ; but among the wasps, humble bees, and 

 ants it apparently occurs constantly (Leucliart). 



