22 



breathed and is now stored up in the tracheae. Further observations are here neces- 

 sary. I only wish to make the following remark: In the winter- larvae of C. mor- 

 sitans which for weeks hang down from the submerged leaflets of water plants without 

 leaving their place I have never seen a flattening or emptying of the tracheae; they 

 are always filled with air and an air-bubble is often seen at the apex of the sipho. 



In his interesting paper (1919 p. 463) KOCH, as one of his main results with 

 regard to the respiration of the Culex larvae, mentions the following: Die Culex- 

 Larven sind Saprozoen, die vorwiegend im Schmutzwasser leben, das infolge der 

 sich darin abspielenden Famines- und Zehrungsprosesse ausserst wenig freien Sauer- 

 stoff gelost enthalt. Die Cufer-Larven konnen nur eine relativ kleine Menge Sauer- 

 stoffes bei der Submersion aus dem Wasser aufnehmen und zur Energieproduktion 

 benutzen. Hoher Partialdruck von 2 (bei niedrigem C0 2 -Gehalt) verlangert zwar die 

 Zeit bis zum Eintritt der Lethargic, bietet aber nicht die Moglichkeit zu einer gros- 

 seren durchschnittlichen Energieproduktion sondern scheint im Gegenteil die Beding- 

 ungen dazu zu verschlechtern. Most probably these statements are quite correct 

 with regard to the larva of C. pipiens; it must however be maintained, that most 

 probably they are quite wrong with regard to all those mosquito larvae which live 

 in natural ponds, often with green bottom, and cannot be correct with regard to 

 the mosquito larvae of those species which regularly hibernate under the ice. With 

 regard to the respiration of these larvae, I refer to C. morsitans. Like many before him 

 KOCH has taken the biological and physiological results relating only to C. pipiens 

 as a prototype for all mosquito-larvae; this is in my opinion inadmissible. 



Used hydrostatic the tracheal system in the mosquito larvae has a loco- 

 motorical significance. The specific gravity of the mosquito larvae is almost that 

 of the surrounding medium; gravity compensation depends upon the size of the 

 larvae, the degree to which the intestine is filled with food, and the condition of the 

 tracheae; every one \v r ho has studied large and small mosquito larvae in a vessel, 

 has almost always had an opportunity to see that the larvae of the first and second 

 moult are mainly or often supercompensated; old larvae after the last moult are very 

 often undercompensated; it may further be shown that larvae in Nature are very often 

 supercompensated, in aquaria with a rich supply of food often or mainly undercom- 

 pensated ; if kept for days in pure water undercompensated larvae will, as the intes- 

 tine is emptied, be altered into supercompensated ones. With regard to the hydro- 

 static function of the tracheal system, KOCH arrives at the following result: Der 

 jeweilige Fiillungsgrad der Tracheen bei Cu/ex-Larven wird einzig und allein durch 

 die physicalisch-chemischen Vorgange bei der Atmung bestimmt; die dabei auftre- 

 tende Gewichtsverschiebung, die wiederum eine bestimmte Anderung der passiven 

 Geschwindigkeit der Larve nach sich zieht, ist nur eine Folge des Atmungsmecha- 

 nismus, hat also keinen Selbstzweck. Der Fiillungsgrad der Tracheen wirkt zwar 

 mitbestimmend auf die passive Geschwindigkeit der Cw/ex-Larven wahrend der 

 Submersion, es muss bei den die Hydrostatik bedingenden Faktoren in Rechnung 

 gestellt werden, aber eine automatische Regulation der passiven Sink- und Steig- 



