344 Miscellaneous. 



sac. This sac is soon formed, and the ova are deposited in its 

 interior. The embryos are rapidly developed, and their escape from 

 the sac appears to cause the death of the female ; at least, Mr. 

 Agassiz has never met with females after their embryos have escaped. 

 The embryos at the moment of issuing from the sac have a triangular 

 outline, their body diminishing rapidly towards the posterior ex- 

 tremity. The development of these embryos presents an example of 

 the most simple evolution observed among the Polychgetic Anne- 

 lides. — Journ. Bost. Soc. Nat. Hist. viii. p. 392. 



Note on the Reproduction of the Larvae of Insects. 

 By Professor Nicolas Wagner, of Kasan. 



Professor N. Wagner has discovered a fact in the natural history 

 of insects which at first sight appears incredible ; but, as it is sup- 

 ported by preparations, the inspection of which by Prof, de Filippi 

 completely convinced him of the truth of Prof. Wagner's observa- 

 tions, a short notice of the singular results arrived at by the latter 

 cannot but be acceptable to our readers. 



In June 1861 Prof. Wagner found, under the bark of a dead elm 

 in the vicinity of Kasan, some whitish apodal worms, the organization 

 of which proved them to be larvae of insects. Each of these larvae 

 was filled with smaller larvae. This was nothing remarkable, as cases 

 of parasitism are well known to be exceedingly frequent among in- 

 sects. But Prof. Wagner was justly struck by the fact that the in- 

 cluded larvae were perfectly identical, even to the smallest details, with 

 the enveloping larvae. By this identity he was led to assume that 

 the included larvae represented a second generation produced by the 

 enveloping larvae. This would therefore be a case of alternation of 

 generations even more surprising than that of the Aphides. 



Improbable as this interpretation may appear at the first glance, it 

 has several circumstances in its favour. Amongst these the principal 

 are the following : — 



1 . It seems impossible to assume that a parasitic larva can pre- 

 sent an organization perfectly identical with that of the organism 

 which nourishes it. 



2. The parasites which deposit their eggs in a single insect, de- 

 posit the whole at once, and these eggs are simultaneously developed. 

 But Prof. Wagner found in one and the same enveloping larva in- 

 cluded larvae presenting the most various phases of development. 



3. Parasitism is an accidental phenomenon, whilst all the larvae 

 observed presented included larvae at a certain degree of development. 



4. The size of the eggs of a given species is constant, whilst the 

 reproductive bodies which here play the part of eggs exhibit very 

 considerable variations of size. 



5. In the interior of the larvae of the second generation a third 

 generation is produced, precisely similar to the first two. 



Professor Wagner has observed three other species of the same 

 genus, all presenting this singular mode of reproduction. The per- 

 fect insects are still unknown. From the appearance of the larvae, 

 they seem to belong to the order Diptera. — Siebold und Kolliker's 

 Zeitschrift, 1863, p. 544. 



