444 Osten Sacken: on the characters ofthe three divisions of 



As the group Lestremina accordiiig to botli Locw and Win- 

 iiertz forms the passage between tlie Mycetoph'didae and Cecido- 

 nii/idae, it will be very interesting to discover the hitherto unknown 

 larvae, and to asccrtain towards whicli sidc their affinity is tending. 



II. The larvae of the second division of the Nemocera vera 

 (Culicidae, Chironomidae, Psi/chodidae, Tipululae) belong to the 

 aniphi-, or metapneustic type with a grcat variety of adaptations to 

 aquatic life. They illustrate a phenomenon which has also been ob- 

 served in other groups of animals (for instance the Crustacea): the 

 great divergence of younger forms produced by various requirenients 

 of adaptation, while the imagos have a closer resemblance. We have 

 here instances of a closed tracheal system (Chironomus, Tanyjms 

 and the aquatic larva of the Ceratopogon, according to Meinert). 

 In Chironomus \) „the tracheal system is rudimentary and completely 

 closed", the larva living in the mud at the bottom of slow streams, 

 quits its burrows from time to time, especially by night, and swims 

 towards the well-aerated surface-Avater by means of looping the body 

 to and fro, and thus procures a supply of oxygen. This oxygen, dis- 

 solved in the blood of the larva is apparently stored up in the „blood- 

 red pigment, w'hich is identical with the haemoglobin of the verte- 

 brate animals". Experiments proved that the larvae could survive 

 a long time (forty-eight hours and longer) without a new^ supply of 

 oxygen. Those larvae of Chironomus which live at, or near, the sur- 

 face „have colorless blood, and a more complete, though still closed, 

 tracheal system". — Corethra likewise has no spiracles, and a very 

 little developed inner tracheal system, probably supplemented by the 

 respiration through the skin (Weismann); besides which there is a 

 hydrostatic apparatus of tracheal bladders, enabling the larva to float 

 motionless below the surface of the water. Culex, Anopheles, Mochlo- 

 nyx have a pair of regulär tracheal longitudinal trunks, inhaling the 

 air through the spiracles. Besides the tracheae, the larvae and pupae 

 of the Cidicidae and Chironomidae are provided with different 

 branchial appendages. The larvae of Psychodd are distinctly am- 

 phipneustic, but owing to the amphibious or subaquatic life of some 

 of them they are also provided with branchiae in various shapes 

 (Haliday, Fritz Müller). The majority of the larvae of the Ti- 

 pididae are metapneustic and terrestrial; many aquatic larvae of 



i) I borrow these interesting facts about Chironomus from the 

 excellent paper of Prof. Miall : „Some difficulties in the life of aquatic 

 insects" (Nature, Sept. 10, 1891). I strongly recommend the perusal 

 of this raost instructive and graphic accoiint of the aquatic larvae of 

 the Nemocera. 



