113 



and when brought into darkness and cold they hung down from the plants for 

 weeks. The biological difference between the C. morsitans larva and the Tceniorhyn- 

 chus larva is in one respect but slight, in another really very large. The C. morsi- 

 tans larva sits with the hooks on the flaps pierced into the cutis of the plant and 

 the apex of the sipho pressed against it; it is only a fraction of a millim. distant 

 from the air-supply of the plant, but most probably it is never able to use it; still 

 it is a question, whether it cannot make use of the air-bubbles which rise from the 

 stem of the water plants in sunshine, from holes w r hich may be pierced by the 

 hooks for the sake of attachment, into the plants. The Tceniorhynchus larva sits 

 with the flaps of the sipho which have been modified into a piercing organ and 

 with the apex of the sipho directly pierced into the air spaces of the plant and is 

 able to use this air for respiration. Still it is a question how much the Tceniorhyn- 

 chus larvae actually use of this air-supply in the \vater plants; for respiratory pur- 

 poses it is, especially in winter, of a very bad quality. (EGE 1915 p. 183); perhaps 

 this air is not their daily food at all, but is only used on certain more solemn 

 occasions (f. i. during the ecdysis process) as the cutaneous respiration is of the 

 greatest significance also for these larvae. If so the difference in the mode of re- 

 spiration between a Tceniorhynchus larva and a C. morsitans larva is not either by 

 any means as great as should be expected at the first glance, the Tceniorhynchus 

 larva being also mainly restricted to cutaneous respiration during winter. After 

 this has been written it was of great interest to me to see that LANG (1920 p. 103) 

 has had quite similar thoughts. With regard to the larva of C. morsitans he writes : 

 "Evidently they shun the surface and may well be on the way to developping 

 similar habits to Tceniorhynchus. Mr. EDWARDS suggests, that it is even possible 

 that that genus may have been derived from Culicella." It has always been main- 

 tained that the sipho of the Tceniorhynchus larva lacks a pecten. In this connection 

 I wish to direct attention to the possibility that the saw teeth in the Tceniorhyn- 

 chus tube may really be the modified pecten. This supposition is weakened by the 

 fact that the pecten in a normal larva sipho is situated on the opposite side to 

 where it is situated in a Tceniorhynchus tube. 



The life-cyclus of the species is probably as follows: The female deposits its 

 hitherto almost unknown eggs in the course of the summer. In autumn the eggs 

 are hatched. In September we mainly find very tiny larvae on the roots. Before 

 winter most of the larvae are fullgrown and in this stage they winter. The pupation 

 takes place in the latter part of May. Whether the imago winters we do not know 

 but it is not probable that it should do so. How to explain the very small larvae 

 in spring I do not know; that the larvae should be biennial would be quite excep- 

 tional. I am more inclined to think that the difficult life conditions render it ne- 

 cessary that not all eggs are hatched in autumn or rather, that not all larvae are 

 fastened under good conditions in autumn, so that the development is delayed and 

 only part of them pass the last ecdysis before winter. 



D. K D. Vidensk. Selsk. Skr., naturvidensk. og niathem. Afd. 8. Rtekke, VII, 1. . 15 



