1915] 
Muttkowski: New Insect Life Histories 
113 
join in the tip of the last abdominal segment; I was unable to 
ascertain this positively, since the apical fans obscure the open- 
ing of the trachea. However, from the fact that the larva car- 
ries but a single air-bubble it may be inferred that there is but 
one tracheal opening common to the two trunks. 
When larvae are submersed a large air-bubble can be seen held 
between the apical fans, which are very favorable for such a 
purpose. It has been questioned whether the prothoracic respira- 
tory tubercles are functional or closed, such as they usually are 
in aquatic insects, at least in the earlier stages. In the present 
form a tiny air-bubble can often be seen attached to the tubercles 
in submerged larvae. This bubble may persist for some minutes, 
but sooner or later it will detach itself and float to the surface; 
this is obviously due to the lack of any means for keeping the 
bubble attached such as found in the caudal fans. 
From the foregoing it seems probable that these larvae obtain 
their oxygen not directly from the air above the culture, but from 
the bubble held enclosed between the apical fans — hence compar- 
able to the respirational method of adult Elmid and Hydrophilid 
and other aquatic beetles. This supposition finds strong addition- 
al support in the method of locomotion. Under the description 
of the larva I have stated that the larva uses the anal tubercle 
in locomotion ; to this may be added that the apical fans probably 
serve a similar purpose. Furthermore, it has been noted that the 
larvae move about actively in the surface film. If we assume 
the necessity of keeping the apical segment and with it the tra- 
cheal opening exposed (i.e., pushed through the surface film) in 
respiration, then the active “looping’ ’ movement of the larva 
becomes a physical impossibility. Also, such structures as the 
pronounced anal quadrifid tubercle and the apical fans lose their 
significance. 
Although this form is like other Psychodas in that it cannot 
withstand a long submersion, nevertheless it is worthy of note 
that specimens left in water for twenty-four hours resumed their 
normal activities; other specimens have been noted alive after 
forty-eight hours, and one lot which was purposely left sub- 
mersed for over four days still showed a few active larvae though 
by far the large majority had drowned. 
The larvae cannot swim although they will go through undula- 
